Personally I try to avoid using the word SJW, much like I don't use words like "feminazis". There are legitimately extreme feminists out there that are out for blood, no doubt, and you could say the word feminazi applies to that specific type of feminist and is in no way a condemnation of feminism as a whole. But when I hear someone say "feminazi", I always wonder if they're using it as a catch-all term to express their disdain for all feminists.
With SJW, I feel the same. When I hear it, I always wonder if the person who's saying it is criticizing a certain type of insufferable people who see social issues where there are none, or if they're hating on even the most legitimate fights for social justice. So I can see why people would be a bit surprised to hear Ethan use it.
That said, it's clear that he's using the word to describe a specific subset of crazy people, not people who fight for social justice in general, so he's still A-OK in my book.