Sounds like exactly the type of play the PSK rule was intended to address.
If I’m not mistaken, it was enforced like this long before psk. On a change of possession, the team in final possession can keep the ball by declining their opponents foul and having their foul enforced, provided their foul was after the change of possession. This is the rule that governs this play.
The foul by R was not psk because it occurred after the kick ended. If it had been psk, and the foul by R occurred before the kick ended, R could still keep the ball by declining Ks foul,but the enforcement spot for their foul would be where the kick ended, where R caught or recovered the kick.