i strongly tend to agree with this. very good observation SBH though we'll never be 100% certain, when u read the text it does sound as if Ammianus is linking the subjects. in fact, ur observation is so correct that anyone daring to disapprove it will have to explain why would have Ammianus used two different terms for an armoured body of men.
i just wonder if this means (bold and underlined part) that 4 Roman scorpions intended to target 4 Persian balistas?