"The barbarians were not assimilated fast enough, and thus brough illiteracy (and indeed an attitude which held that literacy was not a fit pursuit for 'noble' warriors) with them."
The barbarians were probably streaming south to get away from the increasing cold in the north due to the dust veil around the earth that was blocking the sunlight.
And, the Bailey mentioned in the article is an astronomer and a different person than Mike Baillie.
No, the dating is wrong. The claim of is a dust veil c. 540. The barbarians had already detached the Western provinces by the end of the 5th century--hence the 'Fall of Rome' with the decision by Zeno to let Odovacar administer Italy in his name rather than having a Western Augustus.