Do you think the diaspora from Isreal on Ancestry is exaggerated or biased?

I was just wondering, it says
“In terms of the Hebrew Bible, the term "Exile" denotes the fate of the Israelites who were taken into exile from the Kingdom of Israel during the 8th century BCE, and the Judahites from the Kingdom of Judah who were taken into exile during the 6th century BCE. While in exile, the Judahites became known as "Jews" (יְהוּדִים, or Yehudim), "Mordecai the Jew" from the Book of Esther being the first biblical mention of the term.”


I was just wondering, could it be just a guess or is it really that factual or certain? That was a really long time ago, I’m surprised if they were able to know that for certain. How do they know is what I am curious about?