[reg45]

The Persians were not barbarians. Persia was, at that time, a vast empire - far more powerful than the Hellenic civilization.

[Rodamala]

Semanticly, to the Greeks, persians were "Barbarians", outsider, alien, basically "not Greek" cultures. Roman use of the term made it more tribe-specific.

Again... just a matter of semantics in a historic sense.