You're right that "like" would have worked grammatically. "Like", in comparisons, can also be substituted with "as". The owner could have said "He didn't even pee himself, as a lot of people do when they jump," and made perfect sense.

http://www.grammarly.com/handbook/grammar/adjectives-and-adverbs/26/misuse-of-like-and-as/ offers several illustrations of this, including:

"No one makes chocolate cake like my mother does."

Because there is a verb after like (does), the conjunction as should be used. It’s easy to say that about this sentence because as can be replaced by the way.

"No one makes chocolate cake the way my mother does."

 

"No one makes chocolate cake as my mother does."

"Like/unlike" in this sentence grammatically refers to what "a lot of people do when they jump", not to what the cat did or didn't do. Whether you phrase it as "he didn't even pee himself, as a lot of people do," "the way a lot of people do," or "like a lot of people do," it clearly works.

However, "unlike" also works.

This GMAT tutorial demonstrates that we can say things like "Unlike a baked potato, with a full gram of potassium, a banana has only about 600 milligrams."

If he had said, "A lot of people pee themselves the first time they jump; unlike them, my cat didn't," it would have made sense. The problem isn't the "unlike".

There are a number of other problems making that part of the sentence sound "off" -- combining "unlike" with "a lot of people do", instead of with a negative, is a big part of it. "Unlike they do" is an interesting construction, but not a grammatical one. The fact that it's a run-on sentence is also a problem.

You're right that "like" would have worked grammatically. "Like", in comparisons, can also be substituted with "as". The owner could have said "He didn't even pee himself, as a lot of people do when they jump," and made perfect sense.

http://www.grammarly.com/handbook/grammar/adjectives-and-adverbs/26/misuse-of-like-and-as/ offers several illustrations of this, including:

"No one makes chocolate cake like my mother does."

Because there is a verb after like (does), the conjunction as should be used. It’s easy to say that about this sentence because as can be replaced by the way.

"No one makes chocolate cake the way my mother does."

"No one makes chocolate cake as my mother does."

"Like/unlike" in this sentence grammatically refers to what "a lot of people do when they jump", not to what the cat did or didn't do. Whether you phrase it as "he didn't even pee himself, as a lot of people do," "the way a lot of people do," or "like a lot of people do," it clearly works.

However, "unlike" also works.

This GMAT tutorial demonstrates that we can say things like "Unlike a baked potato, with a full gram of potassium, a banana has only about 600 milligrams."

If he had said, "A lot of people pee themselves the first time they jump; unlike them, my cat didn't," it would have made sense. The problem isn't the "unlike".

There are a number of other problems making that part of the sentence sound "off" -- combining "unlike" with "a lot of people do", instead of with a negative, is a big part of it. "Unlike they do" is an interesting construction, but not a grammatical one. The fact that it's a run-on sentence is also a problem.

You're right that "like" would have worked grammatically. "Like", in comparisons, can also be substituted with "as". The owner could have said "He didn't even pee himself, as a lot of people do when they jump," and made perfect sense.

http://www.grammarly.com/handbook/grammar/adjectives-and-adverbs/26/misuse-of-like-and-as/ offers several illustrations of this, including:

"No one makes chocolate cake *like* my mother does."

Because there is a verb after like (does), the conjunction as should be used. It’s easy to say that about this sentence because *as* can be replaced by *the way.*

"No one makes chocolate cake *the way* my mother does."

"No one makes chocolate cake *as* my mother does."

"Like/unlike" in this sentence grammatically refers to what "a lot of people do when they jump", not to what the cat did or didn't do. Whether you phrase it as "he didn't even pee himself, as a lot of people do," "the way a lot of people do," or "like a lot of people do," it clearly works.

However, "unlike" also works.

This GMAT tutorial demonstrates that we can say things like "Unlike a baked potato, with a full gram of potassium, a banana has only about 600 milligrams."

If he had said, "A lot of people pee themselves the first time they jump; unlike them, my cat didn't," it would have made sense. The problem isn't the "unlike".

There are a number of other problems making that part of the sentence sound "off" -- combining "unlike" with "a lot of people do", instead of with a negative, is a big part of it. "Unlike they do" is an interesting construction, but not a grammatical one. The fact that it's a run-on sentence is also a problem.

You're right that "like" would have worked grammatically. "Like", in comparisons, can also be substituted with "as". The owner could have said "He didn't even pee himself, as a lot of people do when they jump," and made perfect sense.

http://www.grammarly.com/handbook/grammar/adjectives-and-adverbs/26/misuse-of-like-and-as/ offers several illustrations of this, including:

"No one makes chocolate cake like my mother does."

Because there is a verb after like (does), the conjunction as should be used. It’s easy to say that about this sentence because as can be replaced by the way.

"No one makes chocolate cake the way my mother does."

"No one makes chocolate cake as my mother does."

"Like/unlike" in this sentence grammatically refers to what "a lot of people do when they jump", not to what the cat did or didn't do. Whether you phrase it as "he didn't even pee himself, as a lot of people do," "the way a lot of people do," or "like a lot of people do," it clearly works.

However, "unlike" also works.

This GMAT tutorial demonstrates that we can say things like "Unlike a baked potato, with a full gram of potassium, a banana has only about 600 milligrams."

If he had said, "A lot of people pee themselves the first time they jump; unlike them, my cat didn't," it would have made sense. The problem isn't the "unlike".

There are a number of other problems making that part of the sentence sound "off" -- combining "unlike" with "a lot of people do", instead of with a negative, is a big part of it. "Unlike they do" is an interesting construction, but not a grammatical one. The fact that it's a run-on sentence is also a problem.