Had a similar moment myself the other day, I was riding clip less, but my left foot was already down on the ground. I was stationary and all of a sudden I toppled over to the right side (fortunately a off road cycle path). I've never in all my years done that, I've been to the same spot before etc, all routine.
I avoid putting any weight to the right in favour of the left, and have done religiously/OCD like since the dawn of cycling. I still have no idea what happened other than "lightness of bike" and adverse camber either that it must be Earth tilting or something