It could be.
In, around or even later than Qin, South was a generally very uncivilized area compared with the Middle Land. The South only possessed preliminary technologies such as planting rice in paddy fields, etc.
南蛮means "Southern Barbarians". That's what it was.
I tend to believe that today's Vietnam might be formed from a couple of ancient "Hundred Viets". Maybe.
That doesn't make sense! If the South only possessed preliminary technologies such as planting rice in paddy fields, etc ... then what is the "Southern Barbarians" meant? Barbarians are such as "planting rice in paddy fields" people?