Welcome to the site and congratulations on having a great kid
After your son thanks his HS coach, he should ask him how the college got his name, where they may have seen him and what it was that created interest in him so that he can follow up with the college appropriately.
This will give him (and you) the answer and also help him follow up properly.
Continue to show appreciation to the HS coach for facilitating the process so that he is likely to continue to do so should more opportunities arise.
Then, make sure he gets back to putting 99% of his attention on enjoying his HS season.
Best of luck and keep us informed.