They were screwed either way. But, they didn't know of Kyle's idol (and falsely thought due to a bad check of his bag).
The scenario that would have happened if they put 3 votes on Kamilla, is that it has been confirmed in a couple places Kyle actually did use the extra vote. So, that would force a 3-3 tie. As has been established, the extra vote carries over to a re-vote. Thomas/Kamilla's votes cancel each other out. Kyle is immune due to the idol play. Kyle sticks with keeping Kamilla and it either forces one of Joe or Shauhin to flip, or they have to go into a rock draw where Kyle (idol), Kamilla and Thomas are immune. The only thing that could have stopped that was Thomas's steal a vote, and either a 4-2 vote on Kamilla (assuming the extra vote gets played) or a split vote.