If you look at Brammeier's Palmare's, he obviously know how to ride a bike. He's been a pro for a long time, been on Pro tour teams, has track experience. Made his national team for Worlds, and has won the Irish National Road Race championship. https://en.wikipedia.org/wiki/Matt_Brammeier

Pretty certain he knows how to descend.

From the Youtube comments, and based upon the riders having trouble with the turn before him, it appears this turn comes up very quickly surprising the riders. (And realize the first time you see this turn is when you're racing through it.)

So Brammeier's pushing it too hard to catch back on, goes too wide on the previous turn, messing up his line for this turn, has to deal with team cars that are cutting off his options, and **** happens.

Obviously, he messed up, but I think there's a bit more to it, than just proclaiming him an idiot.