Nut theft is common in the squirrel world
Squirrels lose part of their stash to squirrel theives regularly.
Thief squirrels will watch other squirrels search and hide nuts. Once the worker squirrel leaves its hidden nuts, thief squirrel will then dig up and take the nuts. Squirrels will hide thousands of nuts in preparation for winter. They can generally remember where they hide most of them but the remainder are either stolen or lost.