It's not like this is a one-off case either. The meme about vegans being this way exists for a reason. Look up That Vegan Teacher[1] for more examples of this behavior.
So it's possible the author had real life exposure vegans.
I'll grant that maybe 50% of vegans aren't raving lunatics. But the ones who aren't raving lunatics need to distance themselves from the raving ones. Maybe call themselves "non-abusive vegans" or something like that. If their didn't all occupy the same label that would be helpful. Of course, the abusers would probably adopt the new lingo too since they're supposedly doing it for your own good. :(
[1] https://www.youtube.com/channel/UC-q4j_ttUgWmir4-Cwh_Hrg