I just watched the replay of the ISU-UCF game on ESPN, and I have to say that I did not see anything from Yarbrough that looked like he was displaying bad "body language". Apparently, none of the ISU fans did either, because his 2nd half benching was apparently a complete surprise to the fans posting on the Redbird message board, and to beat writer Jim Benson of the Bloomington Pantagraph. The only thing close was at the end of the 1st half, Muller took Yarbrough out after his 2nd foul, and he seemed a bit bummed by that. But then ISU was losing by 25 points by then, and everyone on the team looked dejected.
I'm not sure what Muller was referring to. Yarbrough played with good effort, though as noted, he was credited with 6 first half turnovers and was 0-3 shooting. But several of the turnovers were not bad passes, but his teammates just fumbled them away. And he was not the only one missing shots. ISU was 7-24 (29%) in the first half.
I suspect the problem must have arisen in the locker room between Yarbrough and Muller.