"Celt" Conjecture

[M. Demetrius]

but the "Kelt" name was known to Greeks for several centuries

That would seem to me to be a point in favor of the name, not an argument against it.

How many American politicians know the ethnographic map of Iraq?

Probably not many. But surely you don't think the generals in charge are lacking in cultural understanding, do you? It's their very business to know things like that.