Most likely it was done for emissions. The Euro4 1.2 Panda only just makes the 119g/kg CO2 cut for the cheap RFL band and to get there, they needed the thinner oil.I suspect the manual just specifies S2 synthetic as it simplifies stocking instead of having to stock B2, D2, G2 and S2, just stock the diesel version
The non-VVT 1.2's aren't oil critical, so either will be fine from an engine wear perspective.