I think that was a hint of things to come. Maybe in the second half of this season?
http://comicbook.com/blog/2013/10/27/the-walking-dead-what-does-the-voice-on-the-radio-say/
Sanctuary. Those who arrive survive.
Yes, they must be saving it for the 2nd half of the season. Something tells me they'll be moving out of the prison after tonight, and this will be brought up again.