mouthfeel is fuller than you'd expect for finishing at 1.011 and I had thought buttery 'could' be a component but I'm not terribly sensitive to diacetyl. Assumed fuller mouthfeel was from alcohol and hop oils.
Fermentation was in stainless (10-gallon corny) at 66F for 14 days, then 5 days on first dry hop @ ~68F, which seems to also reduce likelyhood of diacetyl?
I don't know much about Pedio behavior - can it turn a beer so quickly?
That seems like enough time for the yeast to clean up diacetyl. Diacetyl has a precursor that is untastable. That precursor can change to diacetyl when the beer cools off. It is possible that the precursor was still in the beer at kegging and converted to diacetyl in the keg.
It's easy to under pitch such a big beer. That can lead to excessive diacetyl.
You can fix it if it is diacetyl. Warm it up and for a 5G batch pitch a 2L starter into it when the starter is at high krausen. Let that ferment out and rekeg as you normally would. I have done this twice over the years with great success.