Calling an unspecified gender person anything other than "they" was until recently considered to be incorrect. "They" is plural but now is used to refer to singlar persons because writing "he or she" everywhere is too much. Calling a user "he" does not imply that users are male or can only be male. Not using "they" or "he/she" or obscure gender neutral pronouns does not make something inherently transphobic. Closing PRs that unnecessarily change pronouns as spam is not inherently transphobic, but the accompanying comment is not very inclusive.
The post talks about "white suppremacist language," but the proposed change did not remove white suppremacist language. It was just a generic anti "woke" message, possibly motivated by people brigading after the original PR to change "he" to "they." White suppremacists may use also use similar language, but you can't just pick things that a white suppremacist has done and decide that anyone else who does the same is a white suppremacist. He's not blameless, but people are intentionally provoking the developer and exagerating the responses for drama.