It's an example sentence under the entry word "shock".
verb 1 [with object] cause (someone) to feel surprised and upset: [no object] experience outrage: he shocked so easily
What does "so easily" mean here?
OP's intransitive usage is relatively uncommon, but it's defined in OED...
shock (verb) also intransitive for passive, to suffer shock.
Here's an example from Google Books...
...talk to Maria Shriver about contemporary social mores and she shocks easily and giggles like a teenager.
But in practice most native speakers would always say she is easily shocked (she's shocked by things that wouldn't normally bother most people). Also note that, idiomatically, we don't use is shocked easily (which has only one instance in Google Books, compared to over 5000 for the first link in this paragraph).
Technically, the writer probably mean, "He WAS shocked so easily." That is, it was very easy to shock him. Most likely the writer means that things that others would find acceptable or just mildly annoying, this person found to be shocking. You might say this of someone who becomes offended and outraged because you used the word "darn".
"He shocked so easily", if read literally, would mean that it took little effort for him to shock others. Either he has little concern about the feelings of others and so does things to shock people with no hesitation, or something about him means that things he says or does with innocent intention, others find shocking.
That said, people do in fact say, "He shocked easily" meaning "He was shocked easily." I think it's grammatically incorrect, but it's common.