Tommy and Tubbo were both getting into an argument with Wilbur/Revivebur. It was obviously about how Wilbur sees dream as his so-called "hero" and how Wilbur worships dream! Tommy was getting so pissed off he is shouting louder

Tommy: STOP WITH THIS STUPID DREAM STUFF, WILBUR!! DON'T YOUNSEE HE'S USING YOU!?!

But Wilbur ignores these things as he rolls his eyes and mocks tommy. That's when tommy and tubbo see the green strings on wilburs wrists and around his neck..