That sounds insane.
Why would you cock a rifle and then pour powder down the bore and then begin ramming in the ball, which could cause the action to trigger?
I think the original meaning was lost somewhere and people just apply it to the genre or weapon they’re familiar with.
With the M-16, I was told to “lock” (a magazine in the well) and “load” a round into the chamber.
Also, there are many varieties of Mouser, as well as other bolt action rifles, that can have the action cycled with the safety applied. It is always recommended that the safety be applied (action locked) before cycling live rounds.