Yes thats true, first of all you should only copy the files that you need to edit.
Just copying everything works fine but isn’t needed because inside the bbPress core is a function whats called Theme_Support ( i believe thats what its called ) And this function does only one thing, before reading all template-files.
Check if the needed template file is inside your theme folder. If it’s not.. –> use the template file inside the plugin folder.
bbPress plugin template files are the default template files but when you copy them over to your theme the new copied files become default.
It’s serious one of the most beautiful and easy constructions I’ve ever seen used at CMS’s. I’ve worked with manny other forum-software that had many more options and features as bbPress but they never had this easy way of safely -editing template files.
bbpress.css works 100% the same copy the bbpress.css file to a folder called CSS inside your theme folder and it works the same way. The forum.css file at the picture isn’t bbPress, thats something I created manually and has nothing to do with bbPress.
Those are two fast screenshots of what I made without having any PHP skills, I just understand HTML + CSS.