I have dealt with fake MOSFets on battery protection circuits before, so there is a market for this. Power MOSFets have usually long lead times, so sometimes the PCB manufacturer can have the good idea to go through a broker instead of the regular distributor.
I have seen cases with rejected MOSFets that were relabeled, and also complete fakes, with a much smaller die placed in a D2PACK chip.
Compare the RDSon between the two boards, it is usually much higher on fakes.