It isn't telling us anything we didn't already know...
ucl.ac.uk
I have a much read copy of 'The Celts' written by Nora Chadwick and one of the maps is very similar to the one published above in a study conducted in 2015:
An international team, led by researchers from the University of Oxford, UCL and the Murdoch Childrens Research Institute in Australia, used DNA samples collected from more than 2,000 people to create the first fine-scale genetic map of any country in the world. Their findings, published in Nature, show that prior to the mass migrations of the 20th century there was a striking pattern of rich but subtle genetic variation across the UK, with distinct groups of genetically similar individuals clustered together geographically.
By comparing this information with DNA samples from over 6,000 Europeans, the team was also able to identify clear traces of the population movements into the UK over the past 10,000 years. Their work confirmed, and in many cases shed further light on, known historical migration patterns.
The term 'Celt' is a 19th century definition that broadly groups Cornish, Welsh, Scots and Irish into a big bowl and stirs up a genetic soup to satisfy the tastes of Nationalists in the era when those nations were close to losing their character through English domination.
DNA testing doesn't tell the whole story and other influences like art, poetry and literature should be taken into consideration. It's a bit like describing the treasure trove found in a lake at Neuchatel and lumping the whole lot under the name 'La Tene' to describe the various tribes and clans that had distinct identities at the time.