Selling a product below its cost of production can be done as a loss leader or market share tactic, but eventually you need to sell things for at least what it costs to make them.

Economic dumping is a specific scenario where one country tries to flood another country with cheap products in a way that usually has some government involvement subsidizing or incentivizing it. Countries are careful to hide these incentives or subsidies when possible because it's an invitation to trade wars. For China specifically, the state takes ownership positions in companies and has no problem forcing companies in the direction they want.