To get to 2078 square feet you have 1750 sq feet above grade and 328 sq feet for a finished basement area. Based on the pictures in the listing this finished basement area is knotty pine walls/tile floor that was being used as a weight room. This 328 square feet is not as valuable as the above ground space in the other house. For reasons I do not understand, the sun room does not appear to be in the listing square feet. In the floor plans in the listing they give the sun room as 14 ft x 9' 7". This would be an addition 134 sq feet of space.

The house that the lawsuit is about is 2600 above grade and 940 sf finished basement. There are no photos of the finished basement in the previous listing, but it does say it has a jetted tub and could be a separate living space.

I generally agree with your analysis, but the size comparison should be 1864 sq ft (giving the sun room) to 2600 sq ft OR 2212 sq ft to 3540 sq ft.