The more I think about it, the more it looks like's he's been hoisted on his own too-clever petard.
His options were:
1. Get Crystal to go along with voting for Matty. This means Corrine doesn't need to play the idol, but probably still would (if it were real) so the idol's out and the game is flipped with him in a four-man alliance on top.
2. Do nothing. If the idol is real, Corrine plays it, Matty is out, and Kenny's alliance is still in a 4-2 position with his biggest in-group competition gone. Since Corrine doesn't have an idol, she's out, and his alliance is 5-1.
3. Vote for Matty, tell Crystal to vote for Corrine. If the idol is real, the result is the same as option 1 except Crystal retains her ability to swing since she's not on record screwing Suzi and Sugar. If the idol is not real, the numbers are the same as option 2 except Kenny's just blown up his own alliance. Best case scenario is that Crystal sticks with him resulting in a 3-3. Which could happen, she's no strategic master herself, but it's not a lot to hang your chances on.
Which is not to say that an underdog team of Kenny and Bob couldn't do some damage themselves. And Sugar is always an open question. But still.