I also fly A320 and reading the above posts:-
1. Ours have standard slides, which as mentioned above, are meant to be used only as FLOTATION devices, they are not like the proper rafts you find on a long-haul aircraft.
2. We use packs off as standard for take off, they go on at 1500 feet when the power is reduced (and we have APU off for take-off). If this was the case here then the aircraft never would have been pressurised. Equally, the packs could have been on for take-off or the APU could have been running supplying the packs but at low level the aircraft still wouldn't have been pressurised.