No, he didn't do it exceptionally because he noticeable slowed down after the second round. We've seen plenty of heavyweights last longer than that while keeping up a good pace - both Cro Cop and Fedor come to mind, as does Big Nog when his fight age wasn't 60+. In today's UFC crop, not so much.. but heavyweights going the distance isn't anything new nor is Cain's cardio.
It's simply hyped and drilled into peoples heads by Rogan every time he fights. Again, he gassed hard in the Kongo fight and slowed considerably in the JDS fight when JDS was nothing more than a punching bag after the first round.
Cain is a very impressive fighter and I think he will dominate the HW division for quite some time.. but his cardio really isn't anything special.