None of which is true. Labour costs in China are rising as their society comes up to Western standards of living and incomes, and besides labour costs are only a small component of the overall manufacturing cost. They have quite strict environmental protection laws too, at a time when the US is weakening its. You can't even build a factory within X km of a protected river now, no matter how much you promise not to release any pollution.
No, the reason the Chinese are able to keep costs down is simple: economy of scale. They have a huge domestic market, and when it comes to EVs they supply the rest of the world with batteries and components, even whole cars that get re-badged.
That and long, very agile supply chains.