Interesting. I thought about the same, and I thought it might be closer to 70% (east and north stands had a pretty good showing).
If we take 65%, actual attendance would have been ~41k. Take 60%, which I think is a low estimate, and you're looking at ~38k.
Considering I saw posts earlier where the guesstimation for attendance at the Utah game was 30k, that's AWESOME.
Also, the Utes really suck.