he seemed annoyed and agitated post the monologue

I mean, when comparing his hosting previous appearances, it seems as if he was ticked off at something later in the show - he started reading strictly from the cue card - no more smiles - and the final farewell was way more hostile than anything he's done in the past.

The conspiracy theorist in me thinks he might have gone off script in the monologue and was told off behind the scenes and perhaps threatened to not be paid his hosting fees if he goes off-script again? Either way - there's no doubt that something was off here.