Just to conclude, my daughter came home tonight and was in the opposite row (middle) to the COS on the aisle. She said he was huge, one of his thighs was the size of both of hers.

The plane must have been oversold by 1 and they were trying to accommodate a father & son without splitting them up (this was a MCO flight). A FA approached him and asked if he give up his extra seat for a refund. He grumbled something like "what's the point of buying two then" but quickly agreed. His very small kid was already in the window and his other small kid joined him from the row behind where he was seating with his mother. She said both kids could fit easily in one seat so comfort probably wasn't a big issue.

I'm sure being a parent and helping out another parent played a large (no pun intended) in this but I thought COS's get a free 2nd seat now irregardless. Maybe he doesn't know the drill being a Disney only flyer?