It was a martian. You see about a billion years ago, the Martian civilization discovered the secret of consiousness. Eventually the robots they created displaced them, and then when the planet's resources were depleted, they left for the stars leaving behind some curators. These curators are not really consious, their robotic creators ensured this so that they would be reliable in their task of preserving their martian heritage, but sometimes they do act in ways that are, almost uncannily lifelike.

This was the case here. The Martian curator bots find the rovers interesting, or rather, they find their controllers interesting. They periodically dust the solar panels so that they will be able to keep roving. They are curious as to what they are doing, maybe even appreciative that someone has visited to appreciate what they have devoted the past eon to preserving. For them, watching us look is most gratifying. They really ache to communicate with us and show us all the Martian history in their underground vaults, but because of their programming to remain inconspicuous, they can't. Still, they are helpful when they can be and not give themselves away.