Good question. The thing is:1 were they fully automatic:2, what type of weapons were they?
Back in the Clinton years, there was a Chinese cargo vessel that was found to have thousands of fully auto AKs.Since the Chinese are owners of America, I bet nobody inspects their ships with any detail.
If they bought that much stuff in one place there is either a big time illegal importer or rogue gun dealer. They damned sure didn’t pick them up at a gun show or from a legitimate dealer.