I've broken both wrists and have probably seen close to 20 others broken, I've seen 4-5 broken exactly like Scott's. They all were from punching something that wouldn't give..... Not saying that IS the case here, but it IS a possibility.
That was my first thought as well. I don't have facebook so I don't know what the break look like, but speaking from my experience of having the back of my hand touch my arm. The only way a wrist would require surgery like that us via a straight on impact that caused the wrist to bend when it shouldn't. Either he punched something, or he had a horrendous fall. Neither of which i'd be out telling people about.