I read the article years ago. The 8,000 is just what I thought I remembered them quoting since they were talking about several thousand years after the invention of agriculture. They might have been more in favor of the Anatolian hypothesis which says the split occurred around 6,500 BC or about 8,000 years ago. Shame I can't find the original article, but it has been many years. The Yamnaya hypothesis is supposedly the more accepted theory nowadays though I am not a linguist. Still a quick search shows it's still debated heavily.

As for the whole Fabius Pictor made it all up has been slowly drifting out of academic favor. Though it does have it's big proponents as well still. First off no one ever stated he made it up and the general knock on history having too much made up family history was very general and not directed at any author, but at the families themselves. Livy nor Cicero quote Pictor when making such statements.

Then on the sources of Pictor, he would have Greek writings that we no longer have access too. Also the Annales maximi. No one knows exactly to the extent he made things up if anything at all. We only have a few fragments to compare. If we had his entire works we could actually see how much he might have made up, is anachronistic, or can be backed up by archeology. Or if his works differ greatly from what Livy or Dio say. I would find it very interesting either way.

On the archeology front I find it interesting that historians have been backing off the entire all of early Roman history was fabricated bit, due to early temples matching the dates they are found in written works (though some not all are incorrect.) The clearing of the forum matching the dates it was in the traditional record. The house of the king having architectural foundations dating to the time of the kings (early kings at that.) And recently a tomb dedicated to a great king was unearthed dating to the 6th century BC this was found in late 2019 putting even further dampers on the people who thought all of early Roman history was fake.

The inscriptions also show that there was indeed monumental writing dating back to the kingship period. So while we don't have access to much of these writings now. Only what we can find. Fabius Pictor would have had access to much more.

It started off with almost all of ancient Roman history was real up to the enlightenment when writers started having serious questions about some very obvious things that were incorrect. Then went to the idea that everything was faked down to even Rome having kings itself. Till several archeological finds had them admitting that some of it at least had to be true. And now more finds showing even more had to be true.

So he and others who wrote after him had to have some sort of record to go off of that went beyond making it up and bad family records as there is no way they get the dates of several temples, public works, and the dating of the kingship period right otherwise just randomly hundreds of years after the fact.