I read that as having land that is not built. Many homes do not have even 1 acre of land they are built on so would not make sense to only allow integers for that question. Or I guess you could round up to 1 acre if below 1. It’ll be clear you don’t own tons of land either way.
I highly doubt it refers to the footprint of the house. 1 acre would be much larger than most mansions.
Unless I’m reading your post the wrong way.