I used to see the crew of his B727 a lot and had a tour of the plane a couple times. Assuming his 757 is decked out nicer than the 727 which was pretty opulent, the weight doesn't surprise me.
Corporate interiors usually weigh in a bit more than airline configurations in similar type aircraft even though there are fewer seats. They can get away with this because the payload is always less so there's more room for extra weight.
Even though they use weight reducing technologies (it only looks like solid wood cabinets) there's a lot of it and it adds up.
Going to go Google that plane now....curious