I think it will be one of these.
You put the end of the loop in the slot when the switch is in the off position. Putting the switch in the on position traps the loop. Pulling the lanyard pulls the loop out causing the switch to go into the off position.
Notwithstanding the comments above, it's a pretty common system and ordinarily quite robust.
Is your RIB tiller steered? If so, the comments above are applicable. If your RIB has a console and you steer from there, the usual way is to have a kill switch on the console and then the fork type lanyard with a spring loaded plunger is a common approach. In this case the switch on the outboard would be mainly redundant.