Yes, he could have responded back though email.
However, college coaches are busy in season, and immediatedly following. It may well be he never even got the email. Or come July 1 or after your son will get a call.
What did your emails include? Should have been an introduction, bio and his summer schedule.
Not too good to put all of your eggs in one basket. Move forward for the summer recruiting period, go out and be seen and concentrate on those who are interested.