That makes sense. North Africa was better integrated into the Roman Empire than Britain was, really, so it wouldn't be surprising to see a fair number of North African Roman citizens, socii, or provinciales in Britain on Roman business.
(see: http://www.caitlingreen.org/2015/04/thanet-tanit-and-the-pho... )
Anyhow, North Africa consisted of Phoenicians (Semitic people, ethnically close to Assyrians who spread out along the north coast of Africa and elsewhere during Classical Antiquity), Greeks, Romans, Egyptians and Africans.
These results are not a surprise as North African kingdoms were very well integrated into the Roman and Byzantine empires. The Romans used to call us the Numidians in the east (eastern Algeria) and the Mauri in the west (west of Algiers to Morocco). The word Moor is derived from Mauri.. The daughter of queen Cleopatra and Mark Antony was married to one of our kings (Juba). Also the oldest medieval skeleton recovered in the south of france is of berber stock, there was even a Roman emperor of North African origin (Septimius Severus).
Anyway, we didn't go anywhere, we're still here, but the way we identify has changed for some of us. Just as the Italians no longer call themselves Romans.
Or should I have listed the specific histories of every part of North Africa from pre-history until the Arab conquests?
And of course, Berber identity has changed throughout the years, after the Arab conquests and Islam spread, Berber and Arab identities mixed, and that gave rise to the current ethnic makeup of the region today.
(That's another rant that many have; it's not like we suffer from too few resources. In fact, we overproduce many costly things. It's simply distribution that's fundamentally broken.)
Also, aren't all people of African origin?
The evidence is found in the oxygen isotopes in their teeth from the water they drank in their early lives, so it's nothing to do with genetics or ancestry and is purely environmental.
There's a huge difference between saying these modern British people have some tiny amount of African DNA and we don't know where it came from, and saying this person right here in this grave from this historical period grew up in Africa. They tell us very different things.
To a point, but that wouldn't be useful in this sort of case. We're talking about people who lived 80 generations ago, many of them before the Saxon and Norman invasions that both flooded the English gene pool. I'm English with no 'known' African ancestry. But it's quite possible I have some African ancestry from 1800 years ago, but I might also have African ancestry from one ancestor in medival times, and perhapse an ancestor from the West Indies sugar plantation days. How would you ever tease that out? It would only add up to a few percent of DNA but would be all over the map. Many brits probably have ancestries all over the place like this. What about ancestors who were Berbers? They have largely Visigoth ancestry, but are from North Africa.
In any case, the idea that this specific evidence isn't of value 'because DNA' is just daft.
The berbers do not have "largely visigoth" ancestry. The berbers are descendents of Numidians and Mauri, and they have a north african origin and the majority of north africans (algeria, morocco, tunisia) regardless of language (arabic or berber) can be identified genetically by the "berber marker." Recent population studies prove the despite numerous military conquests of north west africa there was not a population replacement.
 This is not completely true as we seldom inherit exactly 25% of our genome from any grandparent, but it is usually pretty close.
It's not as simple as that. Do a Google image search for 'Tuareg' and you'll find a number of faces that meet modern British (and American) conceptions of 'black'.
I didn't put it in overly simplistic terms. I said it "is generally not black", not "it is not black" or "it is never black". I was referring to the majority, rather making a blanket characterization about all North Africans.
But the Tuaregs were isolated from that type of immigration?
While not mainland Africa, Madagascar is an example of a migration back into Africa. It was settled by Austronesians from Borneo. Malagasy is an Austronesian language:
That there were Africans in a more modern Britain sooner (just 5000 years ago), is interesting for this reason and it begs the question as to where the population went to-
I'm guessing they married out.
I cannot find a reference, but I seem to remember learning that eighteenth century Covent Garden in London had a significant black population, possibly former slaves freed by and then recruited into the British Army during the Revolutionary War. Within a century, that population had gone, at least as a distinct, visible group: the original population were all male and had taken local wives.
[e.g. I've always wondered why I have epicanthic folds (which are fairly common in the part of Scotland I come from) even though my family has been in Scotland for many hundreds of years, although I think I've found a Finnish connection in the 17th century].