No it's for keeping the ejector rod pushed out.
You fire the gun lever goes down and touches the ejector rod with the square bit in the action which moves backwards and forwards and comes out the front of the action into the knuckle of the forend.
Open the gun, ejects, close the gun and the lock gets cocked again moving the lever up again.
Now you can open the gun without the ejectors ejecting.

Compare it to a Purdey lock where the round pertruding bit of the hammer of the lock, goes in the ejector rod( the bit where it says no2 in the picture)as the position fired/non fired alters it keeps the rod back or pushes it forward.