I did some searching and found some demo videos. In this video, part of the announcement is audible:
https://youtu.be/IcVuubU4BTU?t=90Starting at 1:30, "NOVEMBER SIX HOTEL LIMA, POSSIBLE PILOT INCAPACITATION, SIXTEEN MILES WEST OF KILO CHARLIE LIMA--" at this point the voiceover talks over the announcement, and I have trouble making it out, but I'm pretty sure I hear a "...LANDING ON RUNWAY..." in there as well. For those of you that don't know pilot jargon, that's the plane's registration number (N6HL), the situation, location relative to the nearest airport (KCL-something), and what I'm pretty is a declaration of intent to land on a specified runway.
So, your guess is correct, what the system does is announce its status and intentions and let ATC clear the way.
Other comments have speculated about uncontrolled fields, but I think that's less likely to be an issue. Per the demo video, the auto-land feature requires a GPS approach with altitude guidance published. If a field can't afford a staffed tower, would it be able to afford to have a published GPS approach with altitude guidance? My intuition says no, but as I'm not a pilot, I could be wrong about that. On possible scenario I could see is that the tower isn't 24x7, and so the field is uncontrolled at night. Perhaps such a field would have a GPS approach published, and if the auto-land selected that field, it would be up to any pilots in the area to be aware of the announcement and get out of the way. AFAIK, having one of your radios monitoring the emergency band is considered best practice, so other pilots in the area should be able to hear the emergency announcement and react appropriately.
But at this point, I'm speculating as well. For all I know, the auto land only selects airports known to have a manned tower at the time of activation.