Our theories were:
1.) he was a selfless, sacrificing boyfriend/fiance/husband who was running out to get Chipotle for a hungry girlfriend/fiance/wife and being so self-sacrificing didn't even think about postponing the errand in thinking of his own comfort.
2.) he was playing DDR (or participating in some other form of recreation) and so was warm/hot/sweaty when he left his abode...he didn't realize how cold it was outside until he had completed his errand and was again in the outdoors.
3.) he started off with khaki pants of the zip-off variety, but because he was holding Chipotle he was attacked by two ferocious Chihuahuas who, because they couldn't reach the Chipotle bag, grabbed his pants instead and proceeded to rip off the bottom portion of the pants.
"I mean, if you're going to wear shorts in winter at least wear cool ones...like basketball shorts!"