J. Cole can’t believe what he’s hearing. What he thought was a groupie begging for some stacks is actually a fan and appreciates his music.
This might be interpreted in a different way; basically the whole song up to this point is the pointless type of chit-chat conversations that rappers have with groupies before they have sex with them, and here she basically admits that she’s a groupie, not a fan, since she only knows a couple of his songs but she wants to sleep with him. So his “Word?” is more like, “word, whatever, I’ll still hit that”. This is signaled in the next line when he says “I’ll take it”.
To help improve the meaning of these lyrics, visit "Is She Gon Pop" by J. Cole Lyrics and leave a comment on the lyrics box