This statement is kind of silly. I mean, a bunch of guys in Rome who don't really think that Judea is any more or less important than any other conquered land see an obscure atrological event and think "Oh, this must mean the birth of a kind in Judea". Hardly.
That's not quite correct. The ancient astrologers had divided the sky into different regions -- each symbolizing a particualr nation or race. It's all very complicated. And, I can't remember all the details. But, suffice to say I too had the same objection you raised until I learned a bit more about Astrology at the time of the Romans.