The guy was beaten up by a bunch of fellow "subway angels" (I guess they're like the Guardian Angels group in real life) for not siding with one group (that wanted to split off and go deeper underground) or the other (who wanted to stay "subway angels"). Basically, it was a reflection of the Stranger's origin from that particular story.
I'm not sure if it's in a trade or not. It's from Secret Origins, if that'll be any help.