In the context of the article, it's clear they mean the now common meaning of "barbarian: a person in a savage, primitive state; uncivilized person." TFA even mentions the Romans considered Huns "scarcely human".

Obviously they are not referring to the Roman meaning of "any non-Romans", because that would be a tautology.

Came here to write this. I think it's the headline writer who made the error. The first part of the article just says the Romans thought they acted like animals. So the issue is really what was the culture of the Barbarians.