Me neither. I spent a little time googling to try and figure it out ... these Top 40 radio "charts" only seem to go back 20 years, which sort of makes any record dubious in my mind. I didn't try very hard to figure out what's going on, in the middle of some other stuff ... but uh ... yeah, don't get it either at the point. Stevie Wonder has 10. Usher has 9. Mariah Carey has 9.
Someone better at Google + with more time, let me know if you figure it out. I am assuming one deals with radio play (and is the Top 40 last 20 year one) and one deals with sales as well (Billboard Top 100, the one that is cited for virtually every #1 stat). But that's a pure guess.