Try deleting that person's contact info. Then, add it again. Hopefully once it is added, it will check to see if the person is on an iOS device (which they won't be) and will default to texts.
So they are going to his old phone. I guess he just upgraded it to ios5 cuz he still uses it as an iPod. I tried deleting his contact and adding it again but no luck. I think he is probably going to have to just contact apple.