Nope, just that when people who are not poor live in small houses they live quite well, hardly shocking.

I really dont understand how in America, tiny houses doesn't get translated as slums.

Because what is called tiny house is a status symbol of the middle class. If a poor person lives in a small house or trailer it's called a slum.

I believe there's also a virtue signalling aspect that plays into the problems in the original article.

"I am so dedicated to my work that I willingly turn my home and outside-of-work life into the smallest possible monastic box, using less resources than the average Joe. Plus I'm so classy that it's a beautiful box, and it can't be cluttered by bourgeois garbage because my experience outside work is a stark void and doesn't generate things that would require space."

Whoa, that looks good on your performance review. All you need to add is 'and I'm never there because I work all the time. The only person who sees my house is Merry Maids, and they only have to send one person with featherdusters all over her. She twirls, and that's her job done for the week' ;)

Or the opposite; tiny house permitting made it more apparent that many trailer parks have inadequate septic/sewer systems.

Also see, the resurgence of Hookworm in Lowndes Al.

Is that more a function of density?

It's a function of lower income trailer parks not caring about building and sanitation codes.