That theory has lost a lot of legs in the past few years now that DNA results from ancient North Americans have been sequenced and they don't show any affinity to Europeans, such as Anzick-1 who's body was found in a Clovis burial and Kennewick Man who's skull shape was used as proof by Solutrean Hypothesis supporters. https://www.nature.com/articles/nature14625

If the documentary was older than 2015, it's likely they didn't have this information and would be relying on inferences from the DNA of modern populations, which would be complicated by mixed race people.