It happens. Glad you didn't get hurt.

I swear I've heard the same story a few times though - foot on curb, then fall opposite direction. I haven't done that, but I can see how it'd happen. My advice: Don't use a curb. Just unclip and put that foot down on the road. That way, you're leaning that direction. As you start to ride again, and if anything but straight, it'll be in the direction of your unclipped foot.