Translation:The guards assisted us.
English doesn't use the simple present tense colloquially; you usually have to put it into the present progressive. You wouldn't say The guards assist us; you'd say The guards are assisting us. In colloquial English, The guards are assisting us is perfectly fine for nuboQ 'avwI'pu'.
Unfortunately, Duolingo has decided that in order to distinguish between Klingon progressive non-progressive, all English translations of Klingon progressive aspects will be in English progressive tenses, and vice-versa. This creates a false equivalence. English and Klingon simply don't have the same linguistic tools, so trying to express one in the other always involves approximation. Duolingo is teaching that approximation as if it were exact.
You'll have to always link English progressive tenses with Klingon progressive aspects to satisfy Duolingo. It's not accurate, but it's what we're stuck with.
That extra information on progressive vs. non-progressive in Klingon was very helpful, David. qatlho' !
Same deal. It lacks the specific marker to indicate an ongoing action. Such as the difference between "assisting" vs "will assist"/"assisted".