Kenny could claim to Matty he thought the Matty vote was unavoidable. He just needs to tell Matty about the hidden immunity idol he saw and that Bob and Corinne were set on voting Matty and approached him about it. The only way he could stop the blindside was to find one or two more people to vote for a completely different person in his alliance. He needed Crystal to vote Corinne to flush out the idol so they could be sure they would hold on to the alliance the following week. He feared anything riskier might backfire on him. He's really glad Matty is still around and they will need to vote together this week to flush out Bob's idol and assure final four.

Oh wait he is Kenny, not Penner or Yul, etc. Who needs to keep potential allies/voters happy? I guess not Survivor's greatest strategist