The article clearly posits that investor-owners tend to charge more than other owners, either in resale price or rent, disproportionate to the value of the improvements they make to the property. That is, the article asserts that investor-owned properties cost more than non-investor-owned properties.

Maybe the analysis in the underlying report is flawed (and it very likely could be), but that's the claim. It's not a claim about what might happen, it's a claim about what is happening.