"A whole coke bottle" is most likely referring to "a whole bottle of Coca-Cola" as you say, but the sentence doesn't make sense for a different reason. It's missing something, like the word "spilled", as in:
I accidentally spilled a whole coke bottle.
The purpose of that Urban Dictionary entry is to explain the slang term "wat," and the definition given is "the only proper response to something that makes absolutely no sense."
The sentence was intentionally written to not make sense.
The person speaking doesn't say what they accidentally did with/to the whole coke bottle, setting up the example use of the word "wat" as someone else's response.
Thanks to LawrenceC for providing a link to the specific phrase "I accidentally a whole coke bottle" (and it's usage as part of a larger scope of "I accidentally" phrases used on the internet that lack a verb).