The rule to which I'm referring centres around your location: Spa (treatments, not showers) in Departures lounge is for qualifying departing pax. Spa/showers in Arrivals lounge is for qualifying arriving pax. As your onward/departing flight was shorthaul and you were in Departures, you shouldn't have got a treatment (regardless of the fact you appear to have arrived from a qualifying longhaul - that would have qualified you for treatment in the Arrivals lounge only). They've either changed the rules or you got lucky.