Could blood have gone through what little bit of snow was under him, and into the soil/ground? Not sure how that works
The blood, assuming it's fresh and warm, could melt through the snow where it lands. But it takes a fair amount to do that. Blood spray, say from a gunshot wound or bad enough cuts on an arm, would cool quickly to ambient temperature and stay on top of the snow, but be covered with fresh snowfall.
Small drops, however, would probably penetrate the snow deep enough to be harder to see and would be pretty hard to spot at night. I would normally presume the crime scene people used a UV light, but in this case who knows?
And before anyone worries about how I know this, I'm a hunter in MI. Blood on snow is a normal occurrence. Sometimes, it's not even mine.