How long was your ride? Maybe you had TOO MUCH on. My feet have gone numb after riding for a while because my shoes were too tight. When your feet get warm, they expand. Maybe that combined with the thought of being cold made you think your feet were too cold and thus, numb. uh....

When I ride, I actually only wear one pair of socks (cotton - sometimes wool when it's in the negatives) and a pair of leather adidas (white). Sometimes I'll wrap my feet in a cut grocery bag to keep the warm in.