"Also possible." It's not farfetched, but it's also not why the robots were built. Both things could easily be true at once.

"... Unfortunately, we don't know yet," he concedes, looking back down at his project. "I wish I could give you a better answer than that. All we know is, by the time any of us arrived, the original inhabitants were long gone. And the little evidence we have suggests they didn't go willingly."