What Caused This?

Looks like it got pinched as it was ejected... It can happen.

Ejector starts to spit it out, and as the slide closes, it catches the spent case, sometimes it grips it, sometimes it sends it flying anyway.

May be what happened, may be not. It's a good theory though.

Almost certainly caught by the slide. The ejector throws the case sideways, spinning it. The case also continues back, clips the ejection port, and is damaged as it is knocked away from the gun.