It happened more by accident. I only used the field to compose the "first" comment, but then I hit submit before cutting the text.
At one point a few months ago I tried to do the same in an 'Ask HN' post (not knowing how it was supposed to work), and the text portion of my submission was accepted as a comment on the post that got buried and led to lots of confusion.
Huh, I didn't realise that was possible either. To be fair though, it does say 'or', not 'xor'!
In casual English “or” means “xor” most of the time.
I'm not so sure about that.. it certainly can, and in a lot of contexts it would all or almost all of the time; in other contexts it doesn't.