Yes. Because plurals do not have to use the plural affixes in Klingon. Especially if context or verb prefixes or something else already indicates the number, then the plural suffixes might often be omitted.
Before reading the rest of this, skip to the last paragraph about THE ONE RULE TO RULE THEM ALL. Keep it in your mind as you come back to this point to read the rest. The following discussion might make it look more complicated than it really is. So please look at the very simple rule behind all of this before getting mired in the details.
You could say Ho' qoq and that could mean either the robot admires him/her/it/them or the robots admire them. (You use the null prefix when it is singular third person subject and singular or plural third person object or when it is plural third person subject and plural third person object. lu- is just for when it is plural third person subject and singular third person object. For me, the easiest way to remember it is that when all the subjects and objects are third person, then it is always null prefix EXCEPT when it is plural subject and singular object.)
Basically, I have set up an alert system in my brain to notice if the subject is they and the object is him/her/it. Then I know I must use lu-. Or vice versa if I am translating the other direction. Otherwise if I see he/she/it/they as the subject and him/her/it/them as the object, it is just null prefix. That way I am really just looking out for one special case instead of following many separate rules, which can be confusing.
It makes it really easy because then I do not have to go through the entire list in my mind. I just say do I need lu- to make the Klingon sentence or does the klingon sentence use lu-? If no, then by default it is the null prefix. (Of course I mean only given than all subjects and objects are third person.)
This is equally true when there is no object but a singular or plural third person subject; you will use null prefix.
I call this THE ONE RULE TO RULE THEM ALL: For all combinations of third person subjects and objects including no object, you will use the null prefix with only the exception of lu- for plural subject and singular object.
Although the plural markers (-mey, -pu' and -Du') are optional in Klingon, and are especially unnecessary when the verb prefix indicates a plural noun (like the lu- in this sentence), I have noticed that the course almost always includes the plural markers in the "recommended" translation of a sentence. This sentence, however, seems to be an exception to that trend.
We like to throw a curve ball now and then!
Actually, I think the generally idea we tried to follow was that if the number was obvious within a sentence (like with the lu- prefix) then we did not add the plural markers, and if it was not obvious within the sentence itself (which was many of the sentences), then we used the plural markers where appropriate. I'm sure we wound up with some exceptions to that intent, but that was the plan.