There was an episode of Buckeye Classics that dealt with that season ... and the vote.
Volume 3, Title 1 (if you have the DVDs)
I just re-watched the episode and only heard 2 things that might explain why Michigan expected to go:
1. Bo took a straw vote and was expecting to be chosen, but Illinois changed their vote to OSU.
2. Woody told the players that nobody liked OSU and that they would be at home for the game.