It sounds like Bono might have just remembered the existence of Mofo, muttered a few lines of it before Cobble, got really excited, and yelled at the band until they considered playing it... Adam was probably all for it, Paul McG probably through a hissyfit but might have been forced to shut up eventually, Larry probably grunted in a non-agreeing fashion but eventually gave in, and Edge was probably skeptical but hopefully gave in on the condition that he can still sing falsetto on Stuck this evening.
Then they probably resurrected the Vertigo Tour arrangement and played through it a couple of times. Hopefully they didn't freak out while doing so, but they probably did.