We don't really yet know how good Wyoming is or isn't. Yes, they lost to Idaho, but Idaho had a decent season last year and started this season by taking Oregon to the wire at Oregon. Could mean something, could mean nothing, but simply calling Idaho FCS doesn't mean they aren't any good.
On the BYU side of things, we looked awful, for the most part, on offense vs SMU. It's awful hard to trust a team without an offense to cover a large point spread against anybody.
Look around college football. Teams with a shaky offense can't be trusted to cover large point spreads. Sure, Bama pulled away late, but they were in a 14-13 game with USF entering the 4th quarter. ND and their shaky offense lost to NIU cause they couldn't muster more than 14 pts. Oregon hasn't covered a point spread yet cause their offense is off to a shaky start. OU the same thing.
The fact that we're a 9 pt favorite on the road at Wyoming says the betting public fully believes we'll beat Wyoming. They just don't trust our offense to cover a large point spread. Do you?