Oh, I get it. There was probably no efficient way to move the cursor around with the keyboard. That might explain why users said the keyboard was faster. It was faster for them to push the right buttons. They might have found the mouse cumbersome. They probably thought of the mouse wasting their time.

Do people still consider the results of this study valid? A mouse in 1989 was nothing like a mouse now.

This is the sort of thing the mouse is actually rather good for. Though you're probably better using Ctrl+B to embolden than you are the toolbar or menu.

It sounds like roughly the best case for the mouse and roughly the worst case for the keyboard.