Yeah, I think he did write it himself, bruh.
Listen to these lyrics.
"Ain't nothin' much that you really can tell me
Willie been cold since Benny and Jerry
Must've forgot that I really get busy 
They must've forgot who invented "Get Jiggy," ayy
(They must have forgotten)
Back before there was streaming sales
Way before all the iTunes and the fans had to get CDs still (Hey)
Sixty million records sold, I was on fire, I ain't even need a grill
Did it all with no cuss words, I ain't have to curse just to keep it real (Woo)
Me and Jazz in the late eighties, writin' rhymes, makin' tapes daily 
Fresh Prince make the babes crazy, rest in peace to James Avery
Even when the streets call me corny I still ain't ever let the hate break me
I just wanted the respect first, I still ain't ever let the fame change me (Yeah)"
That sounds just like some Will Smith raps.

Just saying.