What's up with having to specify that the officer would have known the guy had "a clear established right not to be shot?" Doesn't everyone? Is this something that sounds worse than it is because legal language isn't the same as regular language?

Yes, but worse. Generally speaking (and only mildly oversimplifying), if there wasn't a past court case identifying something as a right, it might not be clearly established, so the officer might get qualified immunity even in pretty monstrous situations.

Because that's the literal legal standard for QI being rejected, and no, it's just as insane as it sounds (perhaps moreso once you start digging into it).