Take your hands facing out and make the motion of lifting a barbell, then turn them in and do the same. Notice that your inner chest gets a better "squeeze" from the reverse grip. That is my best guess. I've personally never done this at the gym, but that seems to be the reason. I could be wrong.
Also, it's good to hear that the guy is making it. That sounds like an aweful injury to have at the gym. If he's like the rest of us who go to the gym often, he'll want to be back before they will let him. Just hope he is a little more careful next time.