READ the article again PLEASE. The humans, by applying the principle of free-trade among themselves, out-competed the Neanderthals who I guess used Buchanomics. Any country that turns its back on free trade will go the way of the Neanderthals.
One of the main things that distinguishes Neanderthal digs from Cro-Magnon ones is that Neanderthals only used materials that could be found locally, while modern man could have say, obsidian that was mined maybe hundreds of miles away.
Modern man could communicate and understand new things and ended up filling all the niches much better than the Neanderthals who were always protecting themselves from foreigners.
The adjective is nonsense in this context. Their thesis is that the Neanderthals were outcompeted due to human trade, period. Nothing suggests that the trade was "free" in any sense meaningful to contemporary analogues. If their journal article actually frames it as "free trade" the same way as does this article, then they are subordinating their scholarship to their ideology.
It's unclear, however, why the human ability to organize trading networks would drive the Neanderthals to extinction in any event. Obviously some additional factors must've been involved since otherwise they could just carry on as they had despite their benighted, tradeless subsistence..