I did a short analysis of this order in the news mega here, my take on it was essentially what you summarized. The language leaves open the ability to detain any unhoused person in any facility the state has available for any reason they deem necessary, they already could black bag whoever for "national security", now they can based on mental health criteria that the fascist-aligned Department of Health can make up as they see fit. So while it is aimed at homeless individuals and encampments, it sounds like the order could be used for basically anyone.