Squirrels don't really hoard in the sense trillionaires do ("gathering a great quantity for one's own private collection"), they take seeds and bury them all over the place, which is meaning #2 in the dictionary ("save in one's mind for a future need or use"). The squirrel and other animals eat them later, the 50+% nobody finds to eat can take root. That way, squirrels play an important role in seed dispersal for many species of tree.
I suppose the trillionaire analogy would be they themselves investing money.
I remember reading recently that it had been disproved that squirrels can actually remember where they bury all their nuts and seeds. Maybe some, but quite a lot they cannot.
They end up eating food buried by other squirrels as well as their own.
No, you're ascribing will to a blind and undirected process. Squirrels that survive in recent years and decades bury more food than they ever eat, whether that specifically helped them against certain selection pressures or whether it vestigially remains as a non-impacting behavior.
They hoard until it gets too cold, then they hibernate/hunker down until it gets warm.