about a person in a ghillie suit playing hide and seek near a road which lead to an accident

Did they intentionally try to get hit or cause a crash? If yes, then they bare some (or all) responsibility.

But people wearing regular clothes should not be punished.

We never, EVER see motorists involved in crashed be blamed because they were driving a back car.

This particular crash happened on a lit roundabout where the cyclist apparently had a rear light. The driver was either going too fast, or wasn't paying enough attention.

But where does the responsibillity of the pedestrian end?

This is a good thought experiment. There are legal answers, but logically, blame could be given to a pedestrian when the norms are broken (i.e. suddenly changing lane on a path while oneone is trying to pass).

As a cyclist, or motorist, I make a huge effort to ride defensively. If not to avoid people, then to avoid animals popping out of nowhere.