To be fair if the rest of you is suitably covered, then wearing shorts instead of trousers don't actually make that much difference to me, when I pop out into the garden, or waiting to play footy or whatever etc, and obviously, women do similar all year around.
I don't see the point in it mind, as in I'm not sure what there is to gain by choosing shorts, it just could obviously go badly wrong, especially if you're stood or sat outside for a long time.
The flip-flops thing is ludicrous though, no way is that going to be a benefit to anyone, clearly got a screw loose.
In this weather, if I could only pick 3/4 from gloves, shoes, hat and trousers I'd be picking trousers last though (assuming I already had shorts on).