I have a theory.
The cirlcip came out. As the piston was moving down, it got caught between the piston and transfer bridge, pushing it out and cracking it. At the same time the ring broke, and was pulled around some what. This allowed the ring end to drop into the intake port. As the piston moved back up, the lower ring caught on the top of the intake port, and broke the entire skirt off.
I might be wrong, but this is the only way I can explain everything I see. The only other scenario would have been for the lower ring to have dropped into the port on it's own, but I don't believe the port to be wide enough for that to happen.