"He is seeing us" is incorrect in this context because "to see" is a stative verb meaning you can't use it in the "ing form" as an action of visually seeing someone right now. The German sentence "Er sieht uns" does not give context here to imply "meeting us" as it would with "He is seeing us" used as the 'present continuous with future intention'. So the limited English hints should be changed to the correct form "He sees us" in order to correspond correctly to the sentence in German.
So in the sense of, say, a doctor "seeing us" (in the context of us being able to get an appointment with him), what would the verb be?
I'd probably say something like Der Doktor wird gleich mit Ihnen sprechen (The doctor will speak to you shortly) or Sie können gleich zum Doktor rein (You can go in to the doctor / to see the doctor in a minute), or Ich habe nächste Woche einen Termin beim Arzt "I have an appointment at the doctor's next week".
No one-size-fits-all translation for "seeing a doctor".
Whew! German! I'm getting these things right because they sound right to me I understand far more than I can speak), but don't ask me why I'm choosing one form over another!
I'd call them "not appropriate for this sentence" rather than "incorrect" in absolute terms". sieht can mean "is looking" (e.g. Er sieht aus dem Fenster = He is looking out of the window) and uns can mean "for us" (e.g. Er kauft uns ein Auto = He is buying a car for us).
But in this sentence, they can't mean that.
So the hints can never be suggestions; they're not good enough for that.
Also, I disagree with the translation "he is seeing is"; I think it's the "is" that is confusing the hints system into showing "is looking" first, because "is seeing" is not usually used in English to refer to "using one's eyes".
But this is one of the sentences edited by the Pearson team (see https://www.duolingo.com/comment/24066422 ).
That’s unfortunately not how it works, since the hints are not sentence-specific. They may contain translations that do not apply in the current sentence.
“He is looking at us” could be Er sieht uns an — but this sentence here does not include the an and so “looking at” is not an appropriate translation.