I'm not familiar with that model, but typically the keyswitch connects to the ECU so switching it off shuts off power to the ECU which kills the spark.
Some older small engine type stuff (stuff without a computer) it physically grounds the spark plug wire. Energy prefers the direct path to ground without having to jump the spark gap and the engine dies. This is still how lawnmowers, chainsaws, weed whackers, etc work today.