If you're coasting in neutral, clutch out, slowing naturally to a stop, and you don't touch any of the controls, the only possible input the ECU can be reacting to is the speed sensor (unless I'm missing something).
I suspect the rpm increase is a Euro6 'feature'; I've not noticed this on a Euro5 car, and the Euro 4 Panda doesn't do it either.
On a Euro5 car, if you've got S/S enabled and it's working correctly, the engine will cut as the speed falls below about 5mph. If you're on a downhill gradient, and the speed subsequently increases above about 5mph, the S/S system (if activated) will restart the engine. It will also restart the engine if you make three separate brake applications, regardless of speed.
If you're experimenting at this level, you really should be on a test track, or a private road.