How did the vet visit go?
My guess is that the sponge bath isn't going to affect the healing of his incision at all. The stitches might get infected if soaked in dirty water, but since you avoided the area, I think it will be okay.
As for the pink spot--you said he was in "a state of insanity" when you got home. Could he have scraped it on the inside of his kennel while you were gone?