It's a fair question. I have pondered about this a while ago and here is your anwser:
"That was true; the Bossonian marches, with their fortified villages
filled with determined bowmen, had long served Aquilonia as a buffer
against the outlying barbarians. Now among the settlers beyond Thunder River here was growing up a breed of forest men capable of meeting the barbarians at their own game, but their numbers were still scanty. Most of the frontiersmen were like Balthus--more of the settler than the woodsman type."
Title: Conan - Beyond the Black River
Author: Robert E. Howard
I think Bossonians are the closest thing in Aquilonia to "barbarians". Keep in mind that thanks to D&D influence barbarians are through more as a "class" (like assassin/rogue) than what REH intended. When we take that as a "class" it totaly makes sense for Bossonians ("breed of forest men") as Aquilonians to be regarder as "barbarian class". They are not, however, barbarians per se.
Aquilonia is made up also from Potain (land of warmth and plenty

), Gunderland (best footmen soldiers in Hyboria) and Bossonia (amazing archers and defenders).
As for a bow: Conan was excellent marksman and used the bow often and to a great effect.
"Give me a bow," requested Conan. "It's not my idea of a manly weapon,
but I learned archery among the Hyrkanians, and it will go hard if I
can't feather a man or so on yonder deck."
Standing on the poop, he watched the serpentlike ship skimming
lightly over the waters, and landsman though he was, it was evident to him that the Argus would never win that race. Already arrows, arching from the pirate's deck, were falling with a hiss into the sea, not
twenty paces astern".
Title: Queen Of The Black Coast
Author: Robert E. Howard
It is weird that Conan had to learn the bow from Hyrkanians. If Cimmerians used the bow Conan would have known it. There might be a chances that "archery" is a different art than merely "hunting with bow", but I don't know anything on that subject.