I think he means musical genius, as in proficient at their craft.
We're talking more all-around genius that, like Madden stats up to 99 on the overall intellect.
Who am I to judge? A lot of these guys are very great at displaying their intelligence but there's a process to displaying it too... who's to say how much each rapper (especially in the mainstream) puts into that process
I believe people like Tupac had an intellect that was within them, something that can't be taught - I don't know if this comes from a form of conditioning or some place spiritually

Are you a genius if you aren't good at math?
What if you have a similar AMOUNT of knowledge of a genius but not the type of knowledge that can presented in that way... this is the type of thing that leads most people to artistry

The people you see that are successful in rap represent a true excellence, they're able to transcend societal norms and be proficient in a career that requires much more than talent. Some people with talent can't overcome the stigma it takes to follow your dream. In this country we respect people who follow their dream... once they're successful