It's obviously a combination of a few things.
-Over the course of a number of years, they got his cruising speed way, way up. In the past, he was already at the redline when the kicking started. Now, he's been on cruise control for the whole race so he can throw down much harder. In other words, some of his kick is coming from his accumulated strength.
-He very specifically and consistently worked on running fast with the lactic acid flowing in race situations by racing a bunch of 800's and 1500's/miles indoors and in the spring.
-He changed his race tactics. In the past, he obviously did not have confidence in his kick, and as such, his race tactics reflected it. He was the guy trying to take the kick out of others, and was the victim of sit-and-kickers like Robert Cheseret. Now, he is so comfortable just cruising and knows he can kick, he employs what I could refer to the "Ethiopian women vs. Paula Radcliffe" strategy that involves sitting for longer than you should, kicking in an unreal fashion, and then celebrating in a way that is a little too fresh and happy for the end of what should have been a tough distance race.
The interesting wrinkle will be to see how he is able to kick against runners who are actually at his level, because lets face it, for a guy that finished 10th in the Oly 10k, NCAA competition is simply inferior (in a relative sense). It is one thing to drop a sick last lap off of a pace that is flat out for the competition but cruising for Rupp. The next step is for Rupp to throw down those kinds of finishes off a fast pace.