There are a lot of bad things you can say about China that gonna be true, but it's not well known for running scam call centers - quite opposite.

Authoritorian state with highly controlled internet and financial system isnt exactly a good place for running criminal enterprises.

There just 1.4 billions people in a country and many of them well educated and tech-savvy, so it obvious there just more scammers in total. But I doubt higher percent of population doing scams than average in the world.