I just rewatched the fight. The first two rounds were fairly close. Rory's wrestling made the difference.
Third round was complete domination by Rory. As far as Nate "getting right back up". Rory was letting him do that so he could suplex him. Rory didn't try to put any weight on his back every time he stood up so he could rag doll him.
At no point did Nate come close to out wrestling Rory either. The first round Nate almost hit a switch and Rory immediately hit his own to get part of Nate's back. That was about as close as Nate came to winning any grappling exchanges in 15 minutes. Not something to brag about.
Beating a 155er with no muscle mass when you are a very big 170 is nothing to brag over either. Especially when said 155er has little to no wrestling even in the 155 division.