I found both sides rather aggressive to be honest. The implication that the use of "he" implies that the author assumes every user is male comes with an implied accusation of some form of misogyny.

No, it didn't. Go read the PR, it's extremely polite. I in fact, would challenge you to try and think of a more polite and less accusatory way of bringing up the same issue. I can't.

Furthermore, the "generic he" has also been acceptable English for centuries, and has only been starting to be phased out in the past few decades.

Yeah, you know what else has only been around for the past "few" decades? Literally every single computer and piece of software ever made, you know what literally none of them do? Refer to their users as "he".

You want to make it sound like it's a simple ESL mistake? That's fine you're welcome to believe that, but do you know how I respond to translation mistakes when I'm speaking a foreign language? I laugh and say oops, sorry, my mistake I'll fix that. I don't say "don't bring your politics into this".

I'm sorry but you are making up a fantasy to try and believe that the author wasn't being an explicit asshole.