Michael Milo authored a book about mental health. Adding humans to Wikidata is trivially easy, Mr Milo is relevant as an author of the book so that explains the initial notability.
Given that mental health is not well represented on any Wikipedia, it helps when Wikidata has at least some information. Asking Mr Milo was easy; he can be found on social media, So the source of the information on his profile came in the form of personal communication.
A picture paints a thousand words and Mr Milo promised to upload a photo to Commons. Once we have similar information about all the authors of the book, it becomes easier to write about them on Wikipedia. All the authors are notable in their own right. It just takes someone to write or improve their articles.