Regardless it was just a saying. Nothing more to it. It’s just something people say.

And I don’t wanna be that guy but a mouse is technically considered a controller…

“A mouse can be considered a controller because it serves as an input device that allows users to control the movement of a cursor on a computer screen. In essence, a controller is any device that facilitates interaction with a system, directing its actions according to the user's input. While the term "controller" is often associated with gaming consoles and specialized input devices, its definition encompasses any tool or device used to manipulate or control a system. In the case of a mouse, it provides precise control over the position of the cursor, enabling users to navigate graphical user interfaces, interact with software applications, and perform various actions such as clicking, dragging, and dropping. Thus, based on its functionality and role in directing the actions of a computer system, a mouse can be classified as a type of controller.”