Up until then, they didn't believe that, either.
As for the name "Nazareth," if this find is what they think it is -- I think it's fair to wonder whether the Romans called it something different. Seems to me the Roman name would be the one to look for.
Many of the sites have in fact been confirmed, leading one to believe that John's Gospel is geographically accurate. He also mentions "Jesus of Nazareth" four times (leading one to believe it, too exists).
Adding to the idea of this article, Nathanael said to him, "Can anything good come out of Nazareth?" Philip said to him, "Come and see." (John 1:46) It would make a lot of sense for "a true Israelite" (1:47) to be suspicious of a Romanized town, and those who came from it. (There is reason to believe that Nathanael is the same person as "Simon the Zealot," which makes this even more likely.)