It's a safe bet that they were from the wealthier part of the population, but they wouldn't have to be that wealthy, either. Upper middle class is quite enough to afford a trip to Austria or Italy. We certainly do have enough ski resorts, but I suspect that those are a bit out of fashion with the younger generation. You want to go somewhere fashionable so you can get those selfies that not everybody have. If it was just an urge to go skiing then they could have done that almost everywhere in Norway.
The thing that really irks me about that group is that many of them were health care personnel from Rikshospitalet (main nationwide hospital). Why in the blue hills didn't anyone stop them? Somebody should have known better!