Tis is clearly moisture!!!!! it looks identical to rime icing and its ontop of the wing not the leading edge!! which is where rime icing forms!! now what were the conditions outside interms of met at the time??? are we 10degC or above and with a tempnear the dewpoint?? if so dew/moisture will form! if it has not stuck to th wing it is not ice....its H2O in liquid form........should we de-ice in 12degC and it is raining???? if the capt has done the walk-around during turnaround he/she would hav seen this clearly and touched it to see if was or was not ice. buy the way......its nowhere near the fuel cells!
i would also like to add...........dont think twice.....deice!