Your dog is just practising its instincts of food hoarding that stemmed from their wild ancestors. In the world of early canines (wolves, coyotes, and foxes, etc), food was often hard to come by.
Even if a canine was lucky enough to find some food, he had to compete with other canines in his pack, including other animals, to keep his share of the food. So canines would bury bones near their den. This hoarding was also helpful incase there were leftovers! Burying leftover meat in the soil kept it cool and protected it from sun and scavengers. The soil acts as nature’s refrigerator keeping the food fresher for longer so that in times of food scarcity, the canine could simply just dig it up and enjoy a meal.
If you’ve enjoyed a couple of days exploring and observing wildlife, you’ll notice that dogs aren’t the only creatures that practise hoarding. Leopards drag their kill high up in the tree, to enjoy their meal without the fear of scavengers. Squirrels store their nuts and acorns in a tree hollow and beavers collect piles of vegetation around their lodges before a cold winter.
It’s pretty obvious your dog doesn't need to hunt or hoard his food as a survival tactic like his ancestors, but since this instinct is embedded deep within, it resurfaces from time to time. Because today’s dog will always have his bowl filled and refilled, he doesn't have the need to dig up old bones/meat for nourishment, so chances are that hidden treasures may end up remaining hidden! That’s not much of a problem if the item is not perishable. But if its, its best to keep a watch out as you don't want your dog to be munching on a perished item weeks later only to suffer from an infection or digestive issue. If you are treating your dog with fresh or raw meat and bones, best to ensure they eat them right away.