The nature of computer rankings is such that it takes them a while to catch up with a team that falls off a cliff like BSU did. One sign of this is when a team loses a series of games to teams ranked lower than them....which is exactly what BSU did. In fact, I don't think, for example, the KenPom rankings ever caught up with the magnitude of BSU's crash dive. You might think of BSU's final ranking as sort of an average between the early season and the classic Whitford "stretch run". You could say that's a reasonable portrayal of the totality of the season, but it overstates where they where at the end.
Yeah Sagarin is an interesting example, BSU's season ranking is 136, but Sagarin's Recent Ranking ( uses margin of win/loss and slightly over-weighs the latest games) is 187. This team fell flat when it mattered, and I think opponent scouting, Whitford's inability to deviate from "the process" and lousy in-game coaching had a lot to do with that.