Hi Garion,
The import mapping recognizes the seperate objects in your JSON structure and thus maps those to seperate entities in Mendix.
If you want to use the attributes of those associated objects (e.g. homeMashup.description) in the highest level entity, you would either need to have a different JSON structure (which might be impossible with a fixed endpoint) or you need to have some logic after the initial mapping to map it into a single object.