Would your son tell the coach or just give another reason for declining to play on his team?
I can't name a single College where a Freshman is not offered pot or alcohol, regardless of if they are in an athletic program.
I would HOPE you wouldn't throw away a great opportunity because someone offered to your son what is offered every day on every campus....it doesn't mean he has to partake, it just means he is going to college.
You have to trust that you have raised him to make good choices and have REALLY explained the consequences of poor choices, with maybe a lesson or two on how to get out of that situation if it comes up.
What am I missing here that this has upset you...did you not think he would be offered those things when he got to college? So....it happened during a recruiting visit, well it's going to happen at what ever school he chooses to attend so might as well resign yourself to that fact.