I would think the knife switch theory to be the most plausible and likely, just as 'turn on' ( which has mostly supplanted 'cut on') originally referred to the early stopless rotary switches installed on clothbound peg & pole wiring . I have even heard VERY old folks use"push on the light"-- referring to the two-button ( on button/off button) see-saw type switch that were among the first of the in-wall box mounted switches.