30s also seems high for me, but it's more logical than the eye test or ignoring who you're playing. The crux of it is this - Buffalo has the top scoring offense in the country. Would they if they played Iowa, Northwestern, Ohio State, etc? Of course not. Would they average more than we have? Probably, which is why they're higher in SP+. But not controlling for competition is why college yardage/points stats are garbage. Those work reasonably well within a conference, or in the NFL when the teams are a lot closer together, not overall in college where the difference between Alabama and UMass is astronomical.
I'm sure it's way more complicated than this, but look at it as comparing how well our offense did against each defense, relative to their other opponents. Our offense had far and away the best performance anyone has had against Iowa this year from a yards per play perspective, and right there with the top group in points. By yards and yards per play, easily the best performance against NW too. We've had a couple real bad offensive games against the easy teams (Illinois and Minny), but we've been pretty good against very good defenses over the year. Just not good enough at getting our of our own way.