I will say that Publii clearly is a CMS system since it has the typical structure, as described here https://en.wikipedia.org/wiki/Content_management_system. Okay, it maybe does not have everything that is mentioned as a core feature. If Dreamweaver is a CMS, I don’t know.
How exactly the publishing works, I either don’t know. But if I do only make a small change in a post, it regenerates fast. If I add a new post it has to work some more. Deleting the site and republishing make it use a longer time. So my conclusion is that it does not publish everything each and every time. Remember that if you have a list of the last ten post on every page, then the CMS has to update that list each time you make a new post and that will say that it has to republish/update all the pages. So small changes can make a big publishing event regardless of which CMS system you are using.