Getting swatted is a new thing that trolls do to people who stream their gameplay.
Basically as the streamer is playing, the troll gets a hold of your address, then alerts the authorities about a fake bomb threat at the streamer's address. That's why the SWAT then raids your place.
So the guy wasn't surprised because he knew it had happened to other streamers. Actually, the last famous streamer this happened to, he and his girlfriend were charged because they were in possession of marijuana. Pretty crappy.