I'm sure it's possible it happened, but, yeah, I don't think it's common. IMO blaming "Chinese RCs" is the modern day equivalent of LSD being tainted with strychnine or rat poison in weed, or whatever other nonsensical urban myths that emerged historically to explain small subjective differences in experiences of a given drug. But compared to the various lysergamides which by all reports are very similar (although I am aware, apparently, that some seasoned lysergamide users can distinguish them - although even then not perfectly) and even benzos, to a lesser extent (again, benzo-naive users would be easily fooled), ketamine-like dissociatives in my experience are distinct enough from each other that they could not be easily substituted.
So much this.
I mean, yeah, I could see someone passing off some of the shorter lasting disso RC's as ketamine, but 3-MeO-PCP? Not so much.
That said... much of today's black-market ketamine does indeed come from dodgy Chinese underground labs. Not RC's sold as ket, mind you, but actual ketamine, just shittily made. Ketamine is *massively* popular in China; I don't think even the British do as much of the stuff as the Chinese.
While the Chinese government's crackdowns on illegal ketamine production can be brutal, given the size of the Chinese countryside (where a few bribes can go a long way) it's still a game of whack-a-mole for the authorities.
It therefore shouldn't surprise anyone that the triads are taking advantage of the economies of scale here, exporting massive amounts of black-market ketamine into foreign markets, where genuine veterinary/pharma ketamine has been becoming harder to source due to concerns about abuse.