I wonder what is stopping him from dumping immediately at an international exchange. A dump might be on its way, but there is no reason why the price being transacted now should be very different from the market price of Bitcoin. What happens in the future depends on Chinese regulators.
If there was something stopping him to dump it immediately at an international exchange, maybe the friends of the one who offered cheap bitcoins to OP cannot really convert into fiat something that big from their international exchange because it has limits. That might be the case if it were true but it seems fishy how they are willing to sell bitcoins at a very low price if I were you OP I would just not buy again from him and instead I will dump the bitcoins I bought right away and rebuy at cheaper prices.