Megan, certainly true that a PT6 can feather the prop whilst the gas generator keeps running but I suspect not in this installation. The PC9 and I suspect theT6 had a single power control lever (PCL) and to shut the engine down, a lever or tab in front of the PCL is lifted and the PCL moved ‘over the decent’ and the propeller is feathered and the fuel is cutoff to the FCU. I once managed to have one during shutdown feather when I lifted the PCL over the detent slowly and the gas generator kept running until I moved the PCL back further. Obviously not quite rigged as per the book. There is one reported incident that I am aware of where the PT6A-62 engine in aPC9 failed and both pilots swore that the PCL was moved to shutdown but the prop didn’t feather. They normally would have comfortably glided to the runway but the prop drag meant that they both needed to use the Martin Baker let down. Thankfully successfully.
I also believe that just because the engine fails, the prop will not necessarily feather. If the gas generator isn’t seized it will windmill and provide enough oil pressure to not feather the prop. With no oil pressure the feather weights and ATM will certainly feather it but it depends if the PCL has commanded the prop to feather or there is no oil pressure.