Also, take into consideration that the garage is also included in that 4800 sq ft, the average 2 car garage is around 600sqft. Still a decent size home.
I think the 4,800 sq ft is only the first floor (which has 12 or 20 foot ceilings).
The garage is about 1,200 sq ft, which is where I believe the 5,500 sq ft number came about.
I've only seen photos of the home, but it is very beautiful.