It'd be interesting to see if they could ID which Bolder Boulder shirt it was, narrowing down a year's race.
Then again, my dad did it once when he was out there with work colleagues one year and I ended up having the t-shirt for awhile, which I initially used as a workout shirt and then for a sleep shirt...and I've never done the race, heck, I've not even been in Boulder since I was about 6!
So even if they ID'd the year of the shirt, narrowing the possible registrants, it could be something from a spouse, a friend, heck, even a thrift shop!
Wearing something that he'd not participated in could be a great ruse to look more like he belonged on the trails and not stand out and yet also deflect attention if someone tried to ID him.
Then again, he could have just been thoughtless and actually wore his own shirt, thus really be a great sleuthing tool!