In English, Is “Mansion” a luxurious residence? For example it is with a swimming pool.
In Japan, apartment houses made of reinforced concrete are called condominiums. Even small ones, even plain for low-income people are made of reinforced concrete, it is a mansion. In other words, we refer to the condominium as “mansion”.
On the other hand, wooden apartment houses are called “apartments” even if they are made of advanced building technology.