Translation:Good morning, Omar! Good morning to you, Maha!
The sentence صَباح اَلنّور literally means "bright morning" and is always used as an answer. Ok, it may be kinda unnatural using "to you" in English (I actually don't know as I'm not a native speaker), but we are learning Arabic and I think that using it in these exercises could help us to understand the role of this fine sentence.
I think in English the sequence "Good morning, Fred", "Good morning to you, Susan" (with "to you" somewhat stressed) is very common. So it's not unnatural, and it is an example of the sort of variation that you get in these exchanges. Arabic, obviously, does this using different grammatical distinctions, but the effect is the same.
That makes a lot of sense. Clearly, because these exercises are about routinised greetings, many of the differences -- although they are obviously important -- are pragmatic but not semantic; but the explanations that duolingo gives make no distinction between semantics and pragmatics, so it leaves us learners feeling somewhat demoralised.