In my current surrounding, I encounter riders in masks, backlavas, goggles, ski gloves etc., as if straight from a winter mountaineering expedition, when just a little bit of frost (say -2C) appears. Full-blown hysteria is rampant.
Yes, I noticed that too, and it's really funny. There would also be days that I'd consider t-shirt weather, and yet I see tons of riders on the same day wearing hats, gloves and jackets.... The strangest thing is that I am actually spoiled rotten when it comes to temperature; I get cold easily and detest the slightest discomfort due to cold, so if I think it's t-shirt weather... it really is.
One thing I do notice though, is that when I am about to do some physical activity, my body sort of "wakes up" and can take on things like cold weather, rain, wind, hail etc. On the other hand, if I know I'm about to plop into a warm car and relax, the cold air feels really brutal and I start freezing immediately. So yeah, there might be some psychology at work here. Or you might simply dress differently for driving.