Disk images were the mac equivalent of a compressed folder, e.g. zip. And I find the "compressedd virtual usb-stick" idea a lot more intuitive than the whole "we cram files into other files and loose all metadata" shenanigans.
Apps used to be simple files in the finest unix tradition. No weird installer that does who knows what, no wizards, no special system files, no uninstaller.
Want to take your app from one computer to another? Just send the file.
App stores, installer, and the whole sandboxing gunk, is a million times more complex and unintuitive.
The author seems to be oblivious to the simplicity of the old ways, and thus suspects some hidden magic going on in loading the disk image.
Loading the disk image doesn't do "something" and then displays an IKEA esque installer window. The window is literally a finder window with hidden borders.
The idea was: "If a user can drag and drop files, they can install apps."
The workflow described is composed of several orthogonal concepts that each on their own are super intuitive, or at least were, when unix philosophy, file system usage and user empowerment were still at the core of Mac Os values.