Powder snow on the wing is of no importance. The dangerous thing is rime ice on the leading edge (slats) or just behind it. By the time the air flow is to the flaps, any powder snow will quickly be blown off, as you see here. If the leading edge is disrupted, then the snow on the flaps will remain and not be dispersed, because the flow is already rendered turbulent and separated farther up the wing. Then there is no lift.
My concern was:
1. the aircraft had contamination, "no importance" or not, it's not allowed. It's something that's been drilled into pilots since the PPL, and the ATPL books ramble on about that there must be nothing on the wings at all many times.
2. There could have been inches of ice under that snow and nobody would have known.
I wonder if any officials have seen this. I don't think it should go on pprune and no further.