Starfly,
I do not have information on the specific company that contacted you, but my recommendation would be to research them on the internet.
There is a US company that apparently worked with them on "several brand identity and illustration projects"), it is based in California and I imagine you could contact them. The Chinese publishing industry is huge, they were the "guests of honour" at the Frankfurt Book Fair (the biggest book fair in the world) this year. You could be missing a good opportunity. It is just a matter of being careful until you have enough information to trust (or not trust) them.
Copyright laws are not the same everywhere (and have been changing over the years) but I am sure a lawyer will be able to find the way to protect your rights.
Best,
María
Greetings from Uruguay,
María