He didn't fumble the ball. The clock was stopped due to the RB limping off the field. If it had been fumbled out of bounds, the clock would have started on the snap instead of the whistle, which it was. I thought a run off should have been enforced there too or at least not stopped. The player did the right thing and ran off the field. The official messed up in calling time out. Oh well, thankfully it didn't affect the outcome.