The description says 40 acres. The lot outline on the photos, at least to me, says maybe 10 acres. I mean, if the house is 100 feet wide its like the the lot is 6 houses wide, or 600 feet. And the lot looks square 600'x600'=8 acres give or take.
You have no perspective because it's all desert. The listing isn't going to stretch it from 8 to 40 acres. The desert landscape (or lack thereof) can really throw off size and distance.