#1: That article talks about people from the middle east/west asia who replaced the original inhabitants of Europe. That's why they were darker, before they too had time to respond to selective pressures. But in terms of skin color they're not "black".
"The Neolithic inhabitants were descended from populations originating in Anatolia (modern Turkey) that moved to Iberia before heading north.
They reached Britain in about 4,000BC."
#2: That reconstruction in the picture is specifically "Whitehawk Woman". The artist's rendition isn't even based on her DNA, it's based on the assumption that her people originated from somewhere closer to the Middle East:
"While DNA could not be retrieved from Whitehawk Woman, the ‘Cheddar Man’ team advised that she would probably have had dark skin of a southern Mediterranean/Near Eastern/North African colour, brown hair and brown eyes. This is based on the genetic analysis of ancient individuals dating to the Neolithic from around Europe as well as from Britain specifically."
#3: As humanity originated in Africa, everyone had dark skin at some point if you go back far enough. They would would have lost pigmentation slowly, over thousands of years, as the lack of direct sun creates vitamin d deficiencies and resulting immune system issues. That's a stronger selective driver than skin cancer, which typically takes decades to develop and peaks in the 50s-80s, at an age when most people are dying from something else anyway. Thus the original inhabitants would likely be the whitest, as they have had the most time to adapt to selective pressures.