I think it might matter. I understand the NCAA definition of a booster. Your example of Carmelo/IJ would be a very different case, as it differs in some important details, such as, Carmelo wasn't a high school coach in the Syracuse area having recruited iJ to play for him at the high school level and Carmelo isn't now the head coach at SU.
I'm mostly playing devil's advocate here. I think he is crooked too, but thinking something and proving it are different things. I don't think this case is as clear as you make it. It's not out of the realm of possibility that he only cheated to get him to his high school team, they really clicked together and then when Penny got hired at Memphis, he wanted to continue to play for him. He was likely headed to UK before Penny got the Memphis job - a fact doesn't support the illegal booster activity theory.
Also, under your Penny as a booster no matter any other circumstances view, Penny wouldn't be able to recruit any players to Memphis with whom he had prior contact in his role as a highschool coach or for any other reason, like a camp or instructional session. Given he was a highly successful player, he probably encountered thousands of kids in that way. I'm not sure the NCAA doesn't make allowances for these situations.