That's a "standard" clipless pedal accident. The ones that really get the fond looks from the witnesses are when you're standing around looking cool keeping one foot clipped in (like at a light) and all of a sudden you seem to have shifted your weight to the side that's still clipped in!!!!
Next thing you know you and the bike are in a heap and you can't figure out how that happened....much to the enjoyment of all the pedestrians!