Everyone knows there's nothing Jimmy Fallon likes better than playing games on The Tonight Show. It's his thing. So it makes sense that he'd want Family Feud host Steve Harvey to be on the show as a guest. They can bond over a deep love of televised games.
It also makes sense that if Fallon is going to have Harvey on the show that they'd play a game. And what better game than the one Harvey is intimately familiar with? Yes, they created their own mini Family Feud in the middle of The Tonight Show. Having Harvey host his own show on your show is the equivalent of inviting your masseuse friend of and being like, "Oh hey, what's this massage table doing here?"
The faux show pitted guests Annette Benning and Greta Gerwig, along with Fallon (The 20th-Century Women Family) against Questlove, Tariq, and James of The Roots (The Roots Family) in the suggestive game show that got people screaming "ass" and "testicles."