In the previous game (VB Wario Land), there is a similar case in the haunted mansion level that this bloke mentions (skip to 13:30 in the video below)....
One thing you've got to remember; "blackface" isn't universally acknowledged/understood outside America, since American history is not a universal subject. It got Australia in a lot of hot water a few years back when US singer Harry Connick Jr. came over to judge a classic variety show we used to have every Saturday. Basically, a group of ethnic doctors came on and did a silly tribute for the Jackson Five, with their faces painted black. It was meant to be a loving tribute to Michael Jackson's recent death, but Harry Connick Jr. took it the exact same way as the guy in that WL2 video. After making a huge scene it hit the international press and caused a massive stink.
It's not the first time this sort of thing has happened. I've seen tourists blow up over stuff like one of our best/iconic cheeses, (ironically created by American cheese maker, Edward W. Coon, who created the "cooning process" for manufacturing cheese quicker).
Harry Connick Jr. is just jealous because there will never, ever, be a Harry Connick Jr. tribute show by a group of ethnic doctors