Watched the race.
Rupp didn't run a smart race. He made a big surge between 400m and 500m to move up when the pace up front was really strong. If he had been a little more conservative at the point (the whole pack was running at a good pace) he most likely would have had a bit more left the last 200m.
Obviously I have never ran that fast and it is easy to say from my sofa, but I do know a move/surge early in the race usually costs you later on.
A PB is a PB, so well done to Galen, I think he is capable of faster of he ran a little smarter.