They has been used as a gender non-specific pronoun for a long time. It’s convention whether he agrees with it or not.
Yes, but not as long as all that and
YIKES there's a lot written on the grammar of this. 'Use [of they] for specific known people"
I would argue that they're changing language to make this happen, but that that's ok. I would also argue that most pairs of people will find a reasonable way to get through such things, that most reasonable people won't intentionally insult others, especially others in their workplaces and classrooms. The disunity industry will put such conflicts on the front page, while most of us will adapt and move on.
It's not that big a deal.