Why? Because he can.
Nonconformity is always present in the bike world. It seems like every obsessive cyclist has the primal urge to create their own bike identity. Some do it with their bikes, like the late great Sheldon. Some do it with their cycling attire, like the guys at surly. Some do it with the wrong (in my opinion) tool for the job, like fixed gear mountain bikers.
This guy does it with a combination of all three. He probably drinks his apres-ride microbrews with one of those neon curly straws from the 80's and wears sleeveless turtlenecks in his leisure rides (when he's not contending for the top spot on the Farthing-Cross circuit). While this is purely speculation, we are all a little guilty of our own cycling quirks and post-ride rituals.
Hey, if it makes you happy and makes you ride, go for it.