I am not sure why they used this title for this study as that is not the important part. We already have known Viking was a job description, thats been known for hundreds of years. We also knew that viking settlement was widespread. This study used DNA sequencing to settle the debate on if vikings from certain areas went to certain areas, and if they mixed. It seems to confirm the theory that the norse did NOT mix, and traded, raided and settled different areas separately.
You say "we" knew but the vast majority of people don't. It's not exactly common knowledge among people I know so it's unsurprising a title for general audiences uses it as a hook.
The used that title because more people will see and remember it.
I work in the US with white dudes who literally think their heritage is "Viking" and make it a big part of their identity - I appreciate your point but I also understand why someone might pick that title.
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The title is indeed odd.
The new (to me, at least) idea here is that the different regions of Scandinavia didn't mix as much, "on the job" or genetically, as I thought they would have. They each carved out their own territories and mixed with the local population, but not with each other to a significant degree. It's surprising to find that more genetic material was making it's way back to parts of Scandinavia from those far-flung regions than from neighbouring Scandinavian countries.