Not all (or even many) high schools have rowing teams. They are expensive and time consuming to run, and if there is a club the students can belong to, that often works out better for the rowers and schools. Four rowers (all women) from my daughters’ hs got D1 rowing scholarships, and I know at least one male went to the same D2 school my daughter did, where the AD was a rower so the crew teams were privileged and pampered.
This was from the next season:
When we lived in California, the kids all rowed for private clubs. The hs might have arranged some transportation to practices (they went to one private school and one public school) and they might have formed a ‘hs’ team, but they all practiced with the private clubs. This wasn’t unusual as the same happened for surfing teams or other specialty sports.
I think your son will be just fine being recruited through a club team.