I’ve actually written a paper on an Scordisci archaeological site as part of my High School graduation (maturski rad), so I know more than average Joe about them. What are those historical evidences and sources that show that Serbs as an cultural and ethnic group are continuation of Thracians or Scordisci? Of course local population of the Balkans (already partially romanized and hellenized Thracians and Illyrians) was assimilated by Slavs coming from the north and they are part of Serbian ancestry, but Slavic culture remained dominant for the most part. Have you checked up where those Veneti were located?
When it comes to similarities between European languages, such as Serbian and Irish, yes, ancestors or better said linguistic ancestors of those peoples have lived together. Look up Indo-European language family, everything will be much clearer. Same goes for mythology and culture.
I don’t know what are you trying to prove with that quote. That there were other people living in this region before Slavs arrived?