More often than not, no. Many of these types of factories are intentionally designed to lock workers into a never ending loop, where they're tied in living paycheck to paycheck, often paying rent for a room that's owned by the same company that runs the factory, buying food from a store that's owned by the same company, etc. There are even cases where workers get paid in cash in a custom "currency" operated by the company so there is no way to ever break free after you're in the loop.
Free until you do anything against the company policy. The point stands, the employer controls ever now of your livelihood making the cost of disobedience and switching employment higher.
They aren't being exploited, at least not in the normal way. The Chinese government insists on a zero Covid policy, but they also want to keep the economy running. So you can keep your business running if no one leaves. The alternatives are:
- keep working and earning money, which is why you migrated to the city in the first place. A lot of these migrant workers are bunking it with 4 - 8 other people in one anyway, so it's not like leaving work is some comfy place. But it's more profitable than subsistence farming.
- be locked into your apartment and get no money at all (but still have to pay rent). For the migrant workers who are the manufacturing labor force, that defeats the whole purpose of being in the city in the first place. Besides, they aren't living in comfy apartments.
- the government stop the zero Covid policy so that people can be normal. That's an option anyone but Xi Jinping can take, though.
I've seen some rural villages in Sichuan, and it is definitely subsistence farming. There is not really a feasible way to better yourself besides move elsewhere, so a lot of the parents go work in the city to get a pool of money to improve the lot of their family. Unfortunately, "move elsewhere" is not exactly feasible, either, because of the hukou system, which Mao created to prevent people from moving.
So I'd call it oppression, not exploitation. And it's not the factory owners who are oppressing them, so much as the government. The factory owners are actually providing a means of bettering themselves. (The factory owners might also be exploiting them, but the situation referred to is not an example of that.)