It is very likely the translator did a simple substitution. Given the interconnectedness of the Greek trading world, it's likely that the unit variations were small to negligible in the eastern Mediterranean at that time; probably even less so that during the Renaissance when city-states were vying and fighting each other for commercial dominance.
Having read vol 1 of Braudel's book on the Mediterranean world in the 16th c, units used in commerce varied widely in the 16th century (at least for shipping), and Braudel doesn't even bother in most cases to translate them to modern units, he simply leaves them and compares magnitudes with a few asides to anchor the terms.
(The "mna" has rough equivalents in other ancient Near Eastern cultures. There's at least one "mina" in the New Testament, and in the famous "writing on the wall" at Belshazzar's feast -- MENE MENE TEKEL PHARSIN -- "mene" is basically the same word as "mna".)
By the mean of a thing I denote a point equally distant from either extreme, which is one and the same for everybody; by the mean relative to us, that amount which is neither too much nor too little, and this is not one and the same for everybody. For example, let 10 be many and 2 few; then one takes the mean with respect to the thing if one takes 6; since 10-6 = 6-2, and this is the mean according to arithmetical proportion [progression]. But we cannot arrive by this method at the mean relative to us. Suppose that 10 lb. of food is a large ration for anybody and 2 lb. a small one: it does not follow that a trainer will prescribe 6 lb., for perhaps even this will be a large portion, or a small one, for the particular athlete who is to receive it; it is a small portion for Milo, but a large one for a man just beginning to go in for athletics.
Aristotle, Nichomachean Ethics, Cambridge, MA: Harvard University Press.