"Upper division" in this context-- as in most contemporary usage in the US system, tends to mean course numbers 300-level or higher-- though this is dependent upon the institution/system (UC's system is notable for its idiosyncratic course sequence numbers, for example).
This means, yes, that such courses are predicated on having completed a year or more of college-level study at the discipline; those lower-division courses also serve as prerequisites for upper division coursework.
My daughter has a sufficient number of credits that she
is nearing junior standing, by the way.
Dual enrollment was a good thing for her in high school. Middle school was probably where this problem was at its zenith/nadir, however-- staceychev (and other posters) definitely have my sympathies. A huge block of below-level instruction like that would have just been awful for my DD, I know.
