I understand this is just a footnote in the article, but could somebody explain me what the distinction is that the author is making here? I especially don't understand the italicized "number".
If you build 50 duplexes and 50 SFHs you've got 150 residences. If 50% of the SFHs are manufactured homes then you've got 25 manufactured homes out of 150. If the article is correct there's erroneous claims that manufactured homes are 60% of new "houses" which with my made up numbers would mean there's 90 manufactured homes out of our 150.
From the values of each, you can tell that multi-family units are a larger portion of residential construction. How much larger would require more research as on a per unit basis, multi-family units are cheaper per family than a single-family unit.
Essentially, manufactured home in this case, even if they were 50% of single-family home construction, would be less than 25% of total family units constructed (single-family units + (singe units being construction in multi-family buildings).