I think you’re referring to the use or not, of a CMS!
1) MODx for instance let you and your visitors perform CRUD actions on the web site. The site is dynamic even if the users can’t login front-end. Because when they request the page by url - MODx/PHP go get the page from the database.
2) If you uploaded some .php files to you server manually that did CRUD on a file or database, that is also considered to be a dynamic page...
IMO:
1+2 = is equally secure if you have a secure server.
1 = is less secure if you have a vulnerable server and you install lots of 3rd party applications
2 = is less secure if you have a vulnerable server and if you don’t know PHP very well(!)
The benefit of using systems (with big user groups) is that the code will be tested and fixed by many tired eyes.
The recent WP hack was fixed by an update, if your custom code have a security vulnerability you are by yourself...
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Static pages means no user interaction by forms or urls. You can use .htaccess .htpasswd to present static data for logged in users but it’s just for a one way communication. That is why "static" is safer... but very bad for businesses!