Yes, it is possible that is is an angle shoot, but a very dangerous one. If the other player just says call, he loses the 6000 because his fold would certainly be after the other's call. Also keep in mind, that it is folded around the table after the bet, so he bet into more than one player.
Having the chips stay in the pot is certainly a valid decision, I am sure the player will pay more attention next time.
Georg