Like all of us, he's just human
I once worked at a company where the powers that be decided to go all Scrum. They hired a PM to convert all project, inc ongoing ones, to Scrum. It turned an enjoyable job in to a miserable one.
It's sometimes a more efficient way of building stuff where, for a particular task, you need a whole bunch of knowledge or information that's currently living in somebody else's head.
Also, if I'm having one of those days when I feel sluggish having another person there kickstarts me a bit...
Defaulting to pair programming for every task - especially when the conditions above are not met is a super inefficient and overbearing way of developing though.
source: used to think pair programming was odd until I gave it a proper go.