Well, yes.

He was selling upgrades. But, he thought he was careful enough and that his anonymity was protected. He thinks that maybe UA provided documentation to ebay that selling upgrades/miles is against their TOS and that ebay "ratted him out". But, UA wouldn't confirm how they knew, only that they had "proof". It could also have been a comment from a lackadaisical sponsoree, since UA does often ask questions of flyers on free biz class tickets/upgrades.