How does umidigi kill the flagship brands?

How can a Chinese brand make smartphones cheeper than everyone else? How can they produce a samsung galaxy s20 and sell it for under 250$?
The answer will probably never be answered 100% correctly but in my guess they do what xiaomi and oneplus did before they became famous , if you still not understanding for what brand I'm talking about it's the well talked umidigi .
Umidigi has been called a pretty good brand from well known youtubers in the past like mrwhostheboss he's been talking about the umidigi phones quite a lot as he mentioned them on he's top 2019 smartphones.
Although umidigi can give you a pretty good experience on the high-end tech for not a lot of money they have watches that are destroying flagships like Apple watch and galaxy watch for well under 50$ and smartphones that are killing branding for well under 300$ .