If he had not called that timeout, the penalty would have given USC a first down.
Its really easy to blame the coaches on that play, but it is highly likely that the injuries to the starters shuffled the special teams depth chart which led to confusion.
I do not look at that decision as a terrible one.
Not kicking the field goal on 4th and 1 and then not changing that short yardage play was the biggest mistake. Kalani alluded to that in his post game comments.