A college coach hitting up your son's high school coach is a good sign and an indication that your son has some tools to play at the next level. The summer after Junior year, there were a couple of college coaches that reached out to my son's high school coach. Both had continued interest, but it turned out that neither of the two ended up offering.
But as mentioned above, it may take awhile and getting that first offer is what really gets the turbines moving. 2 different assistant coaches from the school my son committed to watched him at 2 separate showcases in September and November of last year (my son was a HS junior at that time). The head coach finally saw him this past summer at an area code tryout and reached out indicating that there was interest. The offer did not come until the head coach was informed by my son that he had received an offer and also that 2 visits with head coaches scheduled. That's when the head coach made the move and offered my son.
Good luck...it appears you are on the right track and continue reading the advice you get here. I did and was key in being able to help my son ultimately realize his dream of playing baseball in college.