Like someone else said…it looks like one level. My place is ~4,000sqft on 2 levels while I’ve got a cousin who’s house is ~4,000 on one level. You’d think looking at her house it is at least 30% larger with the larger footprint.
Zillow isn’t wrong. The total square footage counting garages and porches may be 19,000 plus, but the actually AC space is what Kenny said. The link you sent even specifies it if you look at the sketch and add up the totals. Definitely not 20,000 sf of actual living space.