I think Cal is a reminder of how little we know about a lot of teams. They went into the Nevada game off wins over UC-Davis(52-3) and Colorado (52-7). I think they said they had the #1 overall defense going into the game and they gave up 52 points to Nevada.
So who knows what that means for other teams this weekend. But what I do know is that Iowa has finished no worse than 12th nationally over the last 3 years in scoring defense and virtually all the starters are back from last year's team so the chance of their defense continuing to be ranked near the top of the nation is much greater than other teams that have blown out inferior opponents to start the season.