Yes, the Dutch are incredibly racist (I’m Dutch, btw) but the “no internationals” isn’t because of the color of their skin but because they don’t stay around for long. With “internationals” (meaning expats and foreign students) you have to go through the hassle of putting up your rental on the market much more often than with non-“internationals”. “No internationals” basically just means “long term rentals only”.

Edit: but, in typical Dutch fashion, this essentially innocent statement is worded as rudely as possible.