I guess I should clarify that when I meant fans, I meant probably hardcore, high-information fans. The general public recognizes Carmelo as a name and that he is a star and do not probably piece it together that he isn't a star anymore. There a lot of non-players who think Carmelo is still really good, but I haven't heard a lot of reputable people say that, outside of players who are probably friends with Melo.
That isn't a knock on your son, it is great that he has an opinion and follows basketball enough to have one. As someone who was once a 16 year old posting on this site, I know I said some really stupid stuff (hey, not much has changed!). On a side note, you bring up an interesting aspect of the new wave of NBA fans and how they consume the product. I play basketball fairly regularly with high schoolers and what Generation Z has to say about basketball in general is very interesting. The influence of Twitter/YouTube is even greater than in the general population and the way they follow the NBA is a far cry from looking at box scores in the newspaper the following morning.