Easy.
Black girls with access to a kid like Boris/Nicole's son......they are probably Cream of the Crop sistas with influential parents and lots of $$$$. Think about how confident and swagged out a 17-year old hood sista is....now give her a trust fund, a stable 2-parent home and a BMW for her birthday.
She's not chasing any dude.
Contrast this with a comparable white girl. Her momma is telling her to nab a winner from Day 1. He probably didn't even have to work that hard to pull her. She might have flirted with him herself.
Parents in this generation figure its better to let Junior figure it out than to force him down a certain path. That's how you end up with a Michael Jordan or Eddie Murphy marrying the lightest sista he can find before cheating on her with nothing but Becky's and then eventually marrying who he wanted anyway when he's 50. Plus dude is hella mixed anyway so it's not like he's going against his race.