You'll get better advice from other people. Here is my $.02
Tell your son to throw strikes & hit his spots. He can't play all 9 defensive positions. Compete and get prepared for this summer, the most important summer of the recruiting timeline.
As the parent you must monitor his health. (I'm not a pitcher's parent.) Count pitches, ice arm, make sure he's not overused or abused on the mound. All the things pitcher parents do.
I think your response so far has been appropriate. Don't draw attention to yourself. It is not about you - but you already know this.
Best of luck to your son.