Well...not really. Bob and Matty made it as far as they could in the game on their own accords. They both failed at winning immunity, but both had to play the game to get up to make it so far in the first place, you know? Bob was absolutely ready to leave before Sugar told him he might have a chance again. For Sugar to interfere with Matty's game like that just to put him and Bob on an equal level...eh, it's kinda complicated, but I still think it was dumb.
But how is that wrong or dumb?
The vote was split among 4 players. Sugar knew she stood no chance at winning. No matter who she voted for, either Bob or Matty was going home. If she voted for Matty, there'd be a tie and a final tie breaker. If she voted for Bob, he was going home.
She didn't actually interfere with Matty's game. Matty's and Bob's game was basically "Whoever wins immunity gets to stay" at that point. But then Susie won it and that was thrown out the window. The vote was split.
Sugar didn't randomly screw up Matty's game. What was Matty's game? Vote out Bob? Well, Bob's was (once Sugar was on his side) "Get a tie for a tie-breaker!". It was a potential 50-50 situation. And Sugar had every right to vote that way. This was no more Sugar screwing up Matty's game than when Sugar was a free agent and tie-breaker at Tribals between two different alliances.
You have a vote, you matter. And unless you have immunity, no matter how good a game you've played, you might very well be going home. If Sugar had voted for Bob, Matty wouldn't technically have won his place at Final 3 due to his own devices. He would've gotten there because
Suzie won immunity. Sugar made it clear that if Suzie hadn't won, her vote would've gone to her, so Suzie would've, at best, faced a tie-breaker (unless Bob or Matty turned on Sugar for whatever reason, but that would not happen as Matty would still want to get rid of Bob).