I think they are confusing the floor (gulvet) with the floor (etasjen) which is more like the third floor of a skyscraper.
Indeed, and all other courses. It's because of a list of automatically accepted "synonyms" kept by Duo, which we can't edit. Frustrating!
There was a bug (atleast on the mobile version) that said "gulvet" means "story" rather than "floor".
Turns out it's been added as an automatic synonym by Duo. We've complained about it, but it has yet to be removed.
If I want to say the boy is lying on the floor will it be : Gutten legger på gulvet?
That would be "Gutten ligger på gulvet".
to lie = å ligge
to lay = å legge