Yes, it is ppsx - see image attached.
Also: on my laptop (where I also have different versions of PPT) when I drag the ppsx file into the PPT program the Morph works, but when I open it by double-clicking the file in the File Explorer it shows a Fade Transition.
So I assume that by double-clicking the ppsx opens in an older version of PPT.
Which still doesn't explain why it behaves as a PPT2013 file on my colleagues' pc that has only PPT2016 installed ...
Anyway, we decided not to work with ppsx files for these presentations
