Allergys? Privacy now that its "normal"? not wanting to pass on a cold? Could be lots of reasons
Discussion
airborne transmission outdoors is essentially impossible.
surgical masks don't stop allergens from getting into your airways (a properly fitted N95 would though, granted. but he's not wearing that).
Privacy maybe.
My hunch though: virtue signalling.
Really though, I don't give a shit why somebody wears a mask outside nowadays. As long as it's not a mandate, it's not my problem.