I think just about all GREAT coaches are stone-faced unless the clock reads 0:00.
I remember when Keith Smart of Indiana hit as dramatic a shot as you will ever see to essentially win the national championship game for Indiana University in NCAA basketball in 1987.
People were jumping up and down but Bob Knight didn't crack a smile or respond in any way, not even for one second, until he saw others reacting & celebrating. Then he started yelling at the players that the game was not over, that there was one second left on the clock after Syracuse had called a timeout, that they need to shut up, sit down, and talk about what to do now.
That sort of focus is part of the greatness (whether you like him or not, and not just Knight, but Belichick, Parcells, Shula, Saban, Wooden, coach K, others)