Reading the description, I don't think Irony as She Is Cast fits. That's for when the actor is cast specifically because their known skills don't match the character's — in this case it's Waititi's background, not his skillset. Maybe Meta Casting instead of Casting Gag, since it's a bit broader than a one-off gag? Possibly with a line about an inversion of Actor-Shared Background?
Incidentally the bullet point for Casting Gag in the description for Meta Casting doesn't seem to match the former's own page description, and several examples appear on both pages. Might be in need of repairs.
Reading the description, I don't think Irony as She Is Cast fits. That's for when the actor is cast specifically because their known skills don't match the character's — in this case it's Waititi's background, not his skillset. Maybe Meta Casting instead of Casting Gag, since it's a bit broader than a one-off gag? Possibly with a line about an inversion of Actor-Shared Background?
Incidentally the bullet point for Casting Gag in the description for Meta Casting doesn't seem to match the former's own page description, and several examples appear on both pages. Might be in need of repairs.