Assuming RDM is going for a logical and real world explanation here, then I think it all comes back to the Song. 'All Along the Watchtower' wasn't written by Anders. It was written by Bob Dylan!
Anything else is libel.
Someone must've included AATW in the programming of the original Cylons on Kobol. And this means Kobol was not really the birthplace of mankind - rather it was some distant colony of OUR Earth. Thousands of years in the future. There's also the possibility that the "colony" of the 13th Tribe is in fact our Earth, and that the 13th tribe were subliminally drawn back there because it was the birthplace of their original programmers.
This explains the map on Kobol, too. Whoever programmed the Kobol Cylons knew that whereever they settled, they would look up into the sky and look for constellations that looked like the old constellations from Earth. The planet in SAGN shared some of those patterns, but not necessarily all of them..
Of course, all of this is assuming that RDM is going for a logical and real-world explanation, which he might not be. But this one works for now.