What conditions was it being run under?
Also, does the rest of your controller look like the one here:viewtopic.php?f=4&t=44226
because that one has some definite QC (lack thereof) problems, including the way the heatsink bar mounts to the case which prevents heat from being able to escape properly, and that would also blow up even genuine FETs. (and it has an SMD resistor just sitting on the PCB, not soldered to anything; probably other issues I haven't found yet, and it has not even been powered on yet).
Another potential problem I see with yours is that it appears to have wrinkles in the kapton tape. If thsoe also exist behind the FETs, they will not sit flat and they cannot get their heat out of the FETs and into the heatsink bar.
Similarly, there appears to be gobs of white paste on there, too, which will do the same thing, as while it is better than air it is not nearly as good as a direct physical connection, and often large gobs also have large air pockets, blockign heat transfer.
There may be other issues, too, but that's what I can see in that single pic.