Total Noob + Other contributing factors
I've been on this section of the Potomac, so have an idea what happened.
First, the river was probably @ about 20,000 cfs, and definitely has big water characteristics, despite the relatively "easy" rapids. Also, the water was prob. 45 degrees or less (on a warm sunny day.)
Anyway, the guy probably put in, and immediately flipped in an eddyline or Class2-3 wave train, swam 15+ minutes (in big, cold, swirly water -- can be quite difficult to reach shore). He hit mid-river rocks right by a popular park-and-play wave. If he had swam for 3 more minutes, the main current would have pushed him right into the shoreline, then the river becomes flatwater.
The guy was clearly a total noob, choosing to paddle alone-knowing that he didn't have proper skills, and requiring rescue from a Class 2 section of river.
Apparrently this kind of thing happens pretty regularly there.