The PLA can lean on factory managers very effectively but they're not going to be interested in small time stuff like credit card numbers. The sort of sophisticated criminal gang doing something like this will have fewer coercive tools at its disposal and I'd imagine would target lower level employees with bribes.

I'm not sure; the DPRK are certainly known to make their espionage units self-funding through credit card fraud.

The problem highlighted in the article is very tricky because verifying a motherboard to that level of details is difficult.

As I hinted in another comment I suspect that they had a suspicion and checked those motherboards very, very carefully.