Yes- and the answer to your question is actually contained within the statement.

"Barbarous".

To us, that means generally uncouth types, but to the Greeks and Romans, it was very specific-Persians and Gauls. The word Barbarian comes from the Greek "babaros". Because people who didn't speak Greek just go "ba ba ba ba".

Split leg pants werent really needed, and could be downright impractical in the Mediterranean. Remember, cloth was a lot less comfortable then.

It also probably relates to horseback riding. The Romans used saddles, but the Celts used only a blanket. Horseback riding, and your prowess on a horse without use of any sort of proto-stirrup device or saddle, was a large part of Celtic culture. In Irish Celtic culture at least, your ech-léim ("steed leap") used to mount a horse was basically your measure as a man. They greatly impressed the Romans, no poor horsemen themselves, to the point of hiring them as mercenaries.

So theres some indication that the Gauls favored pants to protect the legs while riding. Pants were not always worn among the Celts either, they would also wear tunics.

In Rome they were first considered effeminate, then very foreign. Even when shivering legionaries were stomping around Scotland, very few people would wear trousers because everyone would treat you like a weird, gay, kook that had "gone native."