I wrote a longer post and linked to the sibling comment. Yes, they could be autonomous. But there are still issues with that, specifically with the time for the communication to get back "home." (see sibling comment) This doesn't make things impossible, but it definitely decreases the likelihood.

As for within our solar system, I'm fairly certain this isn't true. There would be a crazy amount of effort to hide all that. Like you're hiding an entire civilization from x-rays, visible light, infrared, and radio. A civilization that would be constantly monitored (we pay a lot of attention to local objects). Possible, but these aliens clearly spent a lot of energy and resources to undertake this but have also hidden that resource collection (there's a feedback problem here). Combined with that we aren't sure for mechanisms for life. I'm not going to hold my breath.