Seeing Hawaii, Alaska, Vermont and Wyoming at the top makes me wonder if their definition of "investor-owned" is actually picking up vacation houses/second homes? Just those are all small states with significant vacation housing markets, wonder if that is driving things here.
The article does state they were included, but is it "obviously" true that they should be? Who is more of an "investor", someone who purchases a primary residence to build equity or someone who purchases a second home to vacation in, spending large amounts of money to maintain it and allowing it to sit empty for long periods of time?
In what sense? An investor seeks a return on their investment. The former achieves this. The latter spends money for pleasure. I suppose you could argue that they are an investor seeking non-monetary return, but in that sense everyone is equally an investor, just with different goals.
