That’s the way everybody I know feeds their ferrets. Chuck in a rabbit, hare, squirrels, pigeons whatever and replace it with fresh when the carcass is licked clean.
Ferrets have a tiny digestive tract meaning the food they eat passes through very quickly. A ferret will eat up to 6 separate times over 24 hours so need a constant supply of fresh food. Go and take the ferrets off your friend and give him a slap.
Why would it be dead ? How do you know the cat if that what it was didn’t get spooked by a car or something. Do you often see roe bucks walking about like the one in the video ?