Switching postdoc position (station) in China
Did you go through the process of registering on chinapostdoctor.org? If so, then you are probably right that you are in a system somewhere. However, this should not affect anything because you never actually started your original position.
Nevertheless, I would proactively explain your situation to your current prospective supervisor so they (or their students) will be prepared to help you in case of any snags.
No matter what, it will not be an issue that derails your appointment. If there is an issue, it will be a clerical one that can be sorted out by the school with a phone call or two.