Yeah I get your thought process, but the second vulnerability is actually just how Windows is designed to work. When Notepad follows a link, it isn't opening a web page, it's passing a command directly to the OS shell.
Because Notepad is a trusted native application, it bypasses many of the security checks that a browser has.
If the link uses the file:// protocol to point to an .exe on a remote server, or ms-appinstaller to trigger an install, the OS treats that as a direct instruction to launch that software, so it can trigger an app installation prompt or, depending on the exploit, silently side-load malicious packages.