I'm not sure why David want to side with the improbable, but that is his right.
Other improbable scenarios?
First that the Chinese reverse engineered the 68060. Hitachi managed to reverse engineer the 6809 when they produced the 6309, but the Chinese haven't got a lot to motivate them to attempt this.
Second, that Motorola would license their product and that their spun off successor would be unaware of the arrangement.
Third, that the Chinese would be allowed to produce chips beginning with the MC designation indicating Motorola manufacture.

I don't see any other viable answer to the origin of these chips other then their being re-labeled 75Mhz components.