Hi-Speed Shooting/Slo-Mo Mystery?

My Nikon P530 Bridge camera has several high-speed shooting modes designed to produce slo-mo during playback.

I tested the "HS 720/2x" mode which I assumed would shoot at 50fps (PAL) and playback at 25fps.

As expected it plays back slo-mo in a 25fps project but when dropped into a 50p project it still plays back in slo-mo . . . I was expecting it to play back at normal speed. (Retiming it to 200% makes it play back at normal speed).

Finally I did a VideoSpec scan on the original file expecting it to be 50fps but it is quoted as 25fps . . . yet when played back in a 25fps project (or any other) it is slo-mo.

It can't be shot at 25fps and then play back at 25fps producing slo-mo!

Or is VideoSpec quoting the playback rather than shooting fps?