Translation:How many telephones does the house have?
I would agree with your argument if Duolingo were consistent with requiring us to preserve grammatical structure elements like sentence subject. But usually they defer to what is a more natural English translation. I think either should be accepted. This forced translation sounds more unnatural to me than "I have fear" for "Yo tengo miedo" (which is not accepted because it doesn't sound natural enough in English).
We are moderators, not course contributors, so we can't fix anything.
I'll also be honest. I don't see this as an error. Your sentence is not the same as the given one.
¿Cuántos teléfonos hay in casa? How many telephones are in the house?
The course contributors probably dismissed the reports because they don't see them as the same.
I get that it is not a literal word-for-word translation of the sentence. But is there a meaningful difference between the two? Duolingo accepts equivalent translations all over the place. It seems odd that this is where the line is drawn. A house doesn't own phones. Further, I cannot imagine anyone actually using the "correct" translation in English.
Sometimes it is easier to translate the sentence literally then make the necessary grammatical changes. ie. ¿Cuántos teléfonos tiene la casa? = How many telephones to have the house? literally Therefore "How many telephones does the house have?" Is closest proper English translation
I cannot imagine saying this ever. How many phones does the house have? None. Or maybe as many as you want in it. It isn't like "How many bathrooms does the house have?" That is a fixed number and a feature of the house. Even when people used land lines, you could easily just put in another phone in the house.
Having isn't always about owning. We English speakers very often say a house has.
This house has three bedrooms
That house has a basement
Back when phones were only wired, people often said how many phones a house had. However, I've never said anyone say a house contains two phones. That would be very stilted English.
I think there is still an important distinction here. A bedroom or a basement is a feature of the house. I cannot take the basement out of the house. However, phones are not a permanent fixture/feature of the house. I can put in and/or remove phones from the house very easily. This is especially true given that most people don't even have land lines in their houses these days. The amount of phones my house has now is dependent upon how many people with cell phones are currently inside the house at any given moment (which varies throughout the day).