My guess:
Texas won statistically. OSU was pretty much ***. At TEX or neutral field and TEX wins. That's what it's saying. And PSU wasn't playing anyone impressive enough to jump them. Of course, the original margin matters a lot too. TEX may have been way ahead in the model to begin with.
If I had to guess to your last question - a #8 team would have been expected to beat that Cuse team more handily. Having us #8 was very lofty to begin with. Of course... That and/or another team simply jumped us due to their own performance. But to your original point - how are we even #9 or begin at #8? No idea, but I'll take it lol. I'd guess last year's success, returning starters + recruiting.
Again, this is a statistical model. Process/decision-driven, not binary outcome-driven, as it should be.