It looked like Porter initially was not going to call Kemp safe. he does not point to the plate, he just tosses the ball back to the mound. When Mattingly comes out, the umps confer, then Porter goes over to talk to Davey. Davey says it was Porter's call, and Porter says he saw it, but I'm thinking he was convinced by the other umps in the conversation and is just saying that because it should be his call. I think he yielded. after talking to Davey, he points to the plate to signal the run scored.
It's still incompetence. If I'm right, he should not have yielded to the other umps when it was clearly his call. If I'm wrong, and it really was what he saw, then his mind can't process reality quick enough to be an ump.
I now inform Alan Porter that he is too far from reality.