THE OP DELETED MOST OF THE ORIGINAL QUESTION AFTER REPLIES WERE POSTED.
The original question was much longer and included a lot of details about education expenses.
The answer to the greatly simplified question as it stands now is that "can" means exactly what it says. If you or anyone else can claim your son as a dependent, he must answer Yes to the question "can anyone else claim you as dependent?" It doesn't matter whether anyone actually does claim him. You are not required to claim him as a dependent if you don't want to, but he still has to answer Yes that someone else can claim him.
