People don't walk in straight lines, even though sidewalks and roads may try to make them. Uneven ground, small obstacles and even the vagaries on one's gait mean that the paths we take wobble a bit at the best of times. When getting from here to there is the issue, this means that cutting across a patch of grass or snow will likely not be at right angles to anything.
Urbanists and architects call these paths "desire lines" since they show exaclty where we want to go. Nowhere is that clearer than in snow that's been on the ground for a few days, giving folks a chance to make their own paths. Pity the person who went first: given the depth of the snow it woud have bee a slog. At the time the photo was taken though folks' desires had manifested themselves in a well-trodden track.