It looks like that thread got brigaded by troons. These troon-terrorists cruise around Reddit and search for key words like "transitioning" then they locate the post and alert their perverted friends. It's pretty much the MO of the "against hate subreddits" crowd.

I saw it happen on a sub for gay men when someone made a very mild post when he argued that the trans should be up front about their troonness before a date and specify whether they have a dick or pussy.

Many users showed up that I have never seen before and started imparting their enlightened gender ideology and "genital preference" wisdom. And like a swarm of locust they were gone after a couple of hours when they had downvoted every comment that didn't express sufficient desire to suck the girl-dick and eat the front-hole.