looks very muddy..could have been a blessing and helped slow the aircraft to a halt...i'd hazard a guess..slides used because an airsteps truck may become bogged too..escape slides being a better option, can be used in a non 'evacuation' scenario...(there are various scenarios that slides can be utilized, some without the use of the word 'evacuate' by the crew. In this scenario, crew instruct pax to be orderly/not rush and 'sit and slide' slowly down the slide...as apposed to the 'full on evacuation' which requires urgency and pax to 'evacuate' quickly)
note..speaking from QF perspective.. I am not privy to AirAsia 'procedures'.. different airlines can have different 'procedures'