My guess is that the ice broke off and the fox had no idea. About 30 or 40 years ago Lake Erie froze out quite a way. A bunch of people went to do ice fishing. They drove snow mobiles, dirt bikes, even a brand new Chevy Blazer to get out where they felt they could drill through the ice. At one point someone got tired and decided to leave. It was then they all found out the ice they were standing on was now a free floating berg. The Coast Guard was called and came to rescue the people but their vehicles had to be left behind. But they had no idea they were suddenly on an island.