I agree with Kathie...though she's the resident NA authority; I'm just a DNA dweeb. I suppose there is the possibility that there was admixture, though I imagine it would have been quite minimal and certainly nothing significant, resulting from the 1021 L'Anse aux Meadows Viking settlement (Kuitems, et al. Nature; 2021).
The confusion about 30% European DNA came, I believe, from the rather sensationalist headlines surrounding that 2013 research paper about the ancient remains in Mal'ta that D. Carroll mentioned (Raghavan, et al. Nature 505, 87-91); I even remember seeing specific mentions of the "amazing" connection discovered between NA founding populations and the Welsh, Scottish, and Irish. Sigh.
Problem is, while the research paper was solid (though, back then the best they could achieve was a 1X sequencing depth, which is weak by today's standards) the headlines leapfrogged over several thousands of years of history. Nobody asked, but I'll give my two cents and try not to run too long...
The primary remains, dubbed MA-1, that Raghavan and company analyzed were retrieved from south-central Siberia. The settlement where the remains were found, Mal'ta, is near the southern end of Lake Baikal, essentially where the town of Irkutsk is today, about 100 miles north of today's border with Mongolia. These remains were dated to an estimated 24,000 years (and the mtDNA haplogroup was U, by the way). Another subject was mentioned in the research paper: Afontova Gora-2, dated to about 17,000 years ago and had "similar" genetic signatures to the Mal'ta specimen.
These dates would place them as living in the region during the period of greatest ice coverage--which ran roughly from 25,000 to about 19,000 years ago--of the Last Glacial Maximum, during which time much of Europe and Asia was inaccessible for human travel over long distances. The ice sheets started to decline in the north some 15,000 years ago, which is when the Bering land bridge was likely exposed and NA founder populations entered the Americas.
There was no significant Eurasian emigration west, east, or north during the LGM period of greatest coverage, so it's reasonable to think that the south-central Siberian branch was already in that location before or near the start of the period of greatest ice coverage.
It wasn't until after the LGM that a lineage (over 40,000 years old) called Western Hunter-Gatherer (WHG) emerged about 15,000 years ago (Jones, et al. Nature Communications 6(1); 2015) to populate Europe after the ice age, and they spanned as far as Britain. The other principal genetic group at the time was the Eastern Hunter-Gatherer (EHG); the Scandinavian Hunter-Gatherer, who moved north, was genetically an admixture of the WHG and EHG (Kashuba, Nature Research 2(105); 2019).
Widely dispersed across Europe, the WHG were substantively replaced by successive waves of Early European Farmers (EFF) who migrated in large numbers from Asia Minor into the Balkans during the early and middle Neolithic and through the Chalcolithic around 6,500 years ago. The EFF had a large presence of yDNA haplogroup G, and also E, C, J, H, and T, and were responsible for what we term the Linear Pottery culture in Europe and the Cardial Ware culture along the Mediterranean (Olalde, et al. PLoS Genetics 32(12): 3132-3142; 2015).
Starting around 6,000 years ago and through the early Bronze Age, the EEF in Europe were essentially overrun by a massive expansion of Western Steppe Herders. These invasions are what led to yDNA in Europe being mostly replaced with the R haplogroup (Haak, et al. Nature 522(7555): 207-211; 2015).
That's the very imprecise but very fast run-through of European history from the Last Glacial Maximum to the Bronze Age. And remember, the Mal'ta remains date to 24,000 years ago...almost 10,000 years before Europe saw three, paradigm-changing, population replacement events. Modern Europeans do carry genetic markers from the Mal'ta peoples. But we also carry Neanderthal DNA...which makes up about 2% of European and Asian genomes.
A paper by Joanna Gautney and Trent Holliday (Journal of Archaeological Science 58: 103-112; 2015) did some fancy calculations and came up with the world's entire habitable land area during the LGM as 29.7 million square miles. From that they estimated that the total human population was about 3 million, spread across all continents. Pretty sparse. Today I live in a city that has about 2.5 times the population of the entire world at that time.
What the researchers who wrote the Mal'ta paper hypothesized was that a branch of Western Hunter-Gatherers moved east and interbred with Eastern Hunter-Gatherers before or during the Last Glacial Maximum. It was that same Western Hunter-Gatherer lineage that had already been in Western Eurasia, and then returned after the ice age. There was nothing in the research that ever implied NA founder populations contained modern Western or Northern European DNA, nothing more recent than the ice age. Which DNA was also subsequently spread further east and north into Asia after the LGM, and that traces of it can be found in NA founder populations is in keeping with the Bering Strait migration hypothesis.