Some people find that "motivating". Me? If I am performing well and I know it, that crap is a definite indicator that it is time to move on.
Assuming the coach is a fairly rationale person, and I am not excusing him for failing to be so, he may have been responding to how the mother approached him. There are many parents who will knock a teachers block off if their little darling is the least bit inconvenienced in their scholastic career.
My fundamental position on this is, unless there is more information than indicated, it’s best to let it go. We’ve all had bad moments and none of us deserve fire and brimstone for failing to be the most dignified of people during those moments.