He would have looked like David Walliams in a wig then?

Well I'd say "David Walliams taking the piss by dressing up as Kim Jong-un" would be more what he was going for than falling into the offensive yellow face trope. But Walliams doesn't seem to think anything through. Watching him on BGT you can see he's very much a do it now and think later kind of person.

Still, at least Matt Lucas learned from his years on Little Britain.