I had the same exact thought watching that game, which I'll talk about a bit more in a post I'll put up later tonight.
For all the glazing IU gets, they looked extremely beatable against Iowa, Penn State, OSU, and Oregon the first time around. OSU is probably the closest analogue to an opponent they've played compared to us, except of course we have better trenches and running game. OSU could not get out of its own way. It's astounding that no team scored after the 8-minute mark in the 3rd quarter. At a minimum, OSU should've won that game by ten points.
IU is experienced and extremely well coached. They execute at a higher level than almost anyone. However, they're not 2019 LSU or some behemoth. Mendoza isn't the best QB we've faced, and they haven't seen trenches like ours.