Perhaps. I suspect it may have more to do with the idea that many non-vegans think (whether or not it is true) that vegans believe themselves superior. It isn't unlike how learning that someone is an atheist angers many religious people -- they think the atheists think that they are superior (whether or not they really do).

> many non-vegans think (whether or not it is true) that vegans believe themselves superior.

It's hard to imagine a reason why someone is vegan, that wouldn't logically entail such a self-image.

> they think the atheists think that they are superior (whether or not they really do).

Atheists do not present atheism as an abstention from religion, and generally describe religion as irrational or illogical, not immoral.

Of course everyone who consciously makes a socially difficult choice has a well thought-out reason for it (although atheism is not particularly socially difficult in my environment). But they aren't all directly comparable.