What is the difference in a mansion and a big house? Is it based off square footage or number of rooms? Or is it a mansion if your neighbors say it is…?
Well, part of the Merriam-Webster definition says a mansion is “a large imposing residence”, whereas a house is “a building that serves as living quarters for one or a few families”. So you’ve got the difference between something that’s large and imposing, and something that’s just where people happen to live.
In other words, yeah, it’s a mansion if your neighbors are impressed enough to say it is. 