There are no words to describe this.
Whitewashing, or claiming someone would be prettier if they were born a different race, is not OK.
Whitewashing, like blackface, detracts from the idea that all races, ethnicities, and physical features are beautiful. To claim someone should've been born a different race not only implies the race they were originally born with isn't good enough, it also implies that one race is better than the other.
Unfortunately, Beyoncé has a long history of whitewashing. Earlier this summer, her wax figure was accused of being much whiter than the star is in real life. Additionally, L'Oreal was accused of Photoshopping ads with the singer in order to make her look whiter.
Hopefully, that troll got a much-needed education.