Pretty sad, but here's the prevailing answer:
SQ spokesperson Hugues Beaulieu said the group deviated from the marked snowmobile paths — which are inspected daily — and went out onto the lake.
"They must not have known the area well, because it's an area known for having critically thin ice because of the current," Beaulieu said.
My FIL did some guiding years ago and said that was the biggest headache, trying to keep people from wandering(snowmobiling) off the trails. They don't know the area, especially on a lake like that.