The article explains

> The findings challenge decades of scholarship that played down the importance of migration and emphasized the spread of language and culture between settled populations.“

> “What the genotyping is showing is what the ancient sources report, and what late–20th century historiography has been working very hard to deny,” says Yale University historian Noel Lenski, who was not involved in the work. “We have to … admit the sources knew more than we thought they did.”

If I'm reading that right they are implying academics were pushing the idea of cultural exchange being the most valuable thing, a vague menagerie of local and foreign cultures coming together, rather than a specific set of people arriving from a far off land to dominant an existing empire and influencing the entire region in the process.