What he's describing is Sex Tourism. And that has been going on long before "Passport Bros" (i.e. Black men) was a thing in anyone's minds. Not to say that there aren't Black men traveling for sex/marriage, but they are not as prevalent as its made out to be when it comes to sex tourism.
Older White men are the primary demographic when it comes to sex tourism, and they would be the primary ones to proposition Molly for sex. Not to say that there aren't Black men who wouldn't or aren't. But just like the biggest group of porn consumers are White men and the majority of Sex Tourists are White men, then it stands to reason that if Molly is getting offers, then it's going to come from White men.
She may not be taking them up on their offers, but there's probably more White guys in her sessions propositioning her than "Passport Bros".
And now you know.
EDIT: There's also the fair chance that the one's tipping for the White dildo are White sex tourists looking to proposition her along with White guys watching. And...probably the same group are also tipping for the Black dildo as well (don't want to get into that one).