One of the least productive expenditures of time and energy for a baseball player or parent is attempting to read between the lines on camp invites, emails, and other routine communications to discern the existence or intensity of coach interest.
Baseball coaches are not coy or shy. They do not secretly signal interest through notes on camp solicitations.
If they decide they want your son on their team, they will move quickly and unambiguously to get him on campus and make their pitch for him to commit. Anything short of that means they have at best tentative or contingent interest.
There's nothing wrong with using the note as an excuse to follow up and see if they really know anything about your son. And there's nothing wrong with sending your son to the camp if he wants the high priced group instruction being offered, or he wants to scope out some competition, or he wants a look at the school.
But don't read anything into the note on the camp solicitation.