Koroma beat out a returning senior starter. He wasn't thrown into the situation because of injury or unfortunately, tragedy.
Koroma was a highly touted recruit. One of the top centers in the nation. #25 according to his BYU bio.
Koroma was the only true freshman to start every game at center that year in FBS. Demonstrating that it is typically not an ideal situation.
Additionally, didn't Koroma really struggle that first game? I recall several errant snaps but I could be mistaken.