Yeah I'd say being smart doesn't necessarily help you play good chess - being dumb hurts, though.
I wonder when the last time Gates even played chess? And even though he had way more time than Magnus did, 2 minutes is not a lot of time... Most blitz games are 3 or 5 minutes and if you're not an avid player (or at least used to it) then it's really hard to play fast like that. Magnus probably didn't have to think at all since he already knew the opening, whereas Gates was probably on his own from the third move on.
Skill in chess requires (at Carlsen's level) a great deal of intuition and knowledge and practice. Bill Gates is a talented programmer and businessman. Unless chess was a personal passion or interest, there would be no reason to expect him to be any better than the average person under pressure, faced with a 2-minute clock and a world champion.
Yeah because chess is an INCREDIBLY hard game to get good at regardless of how smart you are. I've been playing for years and going to my local chess club and I'm still trash ahaha.