If you clicked on it immediately after he was sold, then it doesn't matter anyway how he played or if his rating while he played for you changed. What would matter much more is if a player that is of same team skill and manager as you are takes him and then makes such results in the next games. It could be a visual bug too, because as you've said, the stats of how he played, aka ratios, changed. That doesn't matter, does it?

It could also be a bug that changes a players ratio upon purchase. For example, if the player is woth 1 M and you sell him after a big bidding competition for 5 M, the game automaticly turns him into a player thats worth 5 M and with it the ratios? It could be unintentional, but we can't know that. Your assumptions are legit though.