@Clarence.
Previously I had said that you need to make sure how much you're jamming for before you jam and I do stick by that, "You got about 16k?" If he says yes and turns out to have $16.9k then you've prolly just gotta be a bit tilted at him but if he says yes and then turns out to have 20k well then you're perfectly in your rights to say you're only paying him 16, IMO. IT is a mistake you made just gotta learn and move on, you'll likely never do this again, we've all been there.
All that being said, the facts you make about him adding chips when you're supposed to inform the production, coupled with the fact he'd been losing I can see how you made the mistake
It seems to me he was losing big in the game, snuck chips onto the table so people wouldn't think he was losing, not defending him from the accusastions but it does feel like this was an ego driven decision not an attempt to cheat. What a clown though, playing HS for years has he never lost 400-500 big blinds in a live game before, pretty sure Ivey has gotten buried a few times in his career and he's widely considered to be quite the cardsman.
What is HORRENDOUS though, is when he approaches you to "sort this out" - you assume he's going to offer you some of the money back (although stupid to do this before the hand as you could have won the pot) the equity share of the extra money seems very fair offer from you actually, he offers you the chance to BUY A PIECE of him in an upcoming cash game...
Jesus christ what a huge bellend.