It's very disappointing that such a talented person was pushed out, especially someone like Chris who seems to be a genuinely good person. It's all too common to see brilliant founder types be pushed out by power- and influence-grubbers who end up ruining the original spirit of the project. I read through one of the threads he linked that was producing "more heat than light" [1] and, yeah, it's easy to see why he'd move on. The person responding to Chris wasn't adding any value to the discussion, just being a pedantic troll. What's worse is that person was a moderator.
Reading this thread for the first time, it looks to me like (1) everybody is fairly well behaved by the standards of an online forum and (2) Chris is probably using more inflammatory language than anybody else.
So maybe one the problems is that at this point, he's no longer getting the deference from other community members that he feels he's still owed?
[1] https://forums.swift.org/t/if-let-shorthand/54230/188