It's not "gathering" if you're taking things that someone's deliberately prepared for their own future use.
It doesn't fit nicely in our societal view of "yours" and "mine", but whenever you take something, whatever it is, you are almost always taking it away from something else. Surely "thieving" is gathering. It's just a kind of gathering that society has decided is not okay, except in all the cases where society says it's okay, like taking the animals home, or the native humans, and so on.
Didn't many berries evolve so that animals would eat the berries and their seeds would end up in their feces? I'm not sure how to say that without it sounding like a cause and effect. Plants didn't _intend_ to evolve so that animals would eat the berries and carry their seeds away, it was more a symbiotic relationship.
If this guy got shot stealing from people, we wouldn't just call it killing; because we have a philosophical framework about justice and retribution. If you were consistent, you'd have to be okay that this guy would be treated like a fox who raids a henhouse; up to the personal whims of the aggrieved.
From the hermits point of view, outside of the society with its philosophical framework, it is just gathering.
Society may call this theft. I may also jell at the crow stealing my unwatched food "you thief, give me back my food!". That is from my point of view, not the crows'.
To society the hermit still is human and we have morals and ethics that shall prevent us treating him as just a raiding wild animal / fox.
The plant isn't someone.