We don't know all the details yet, but the airport was VFR so my expectation is that they were VMC.
The majority of arrivals I've flown at FDX have been Visuals backed up by the appropriate approach.
Assuming the FMS is the same iteration as FDXs, can't really plug in a path on the visual the way it sounds like you can. But, the FMS will build a vertical path based on the instrument approach you have loaded up---so, for FDXs, it would have generated a path consistent with the PAPI for 18.
There's been some discussion of PAPI useage, quite frequently you can see them for forever and a day, but they are only good for terrain clearance close to the airport (4SM to be precise-although 4NM for a VASI----things that make you go hmmmm, in AIM)
As the factual data comes out, will be interesting to see what their G/S was. Steeper than normal approach, slight TW reported, doesn't take much of an aimpoint shift to trigger a sink rate call out