Hi,
Welcome to our community! 
The player collides with a collider, not with a wall or the ground or something else. If the wall collider and the ground collider are the same, they are not considered different collisions because the collider is the same.
The periscope works because the platform collider is an edge/outline collider. See the Tilemap collider. “Outline” means that the collider does not have an inner part. It is just the edge. When the periscope collider touches the edge, a collision happens. When the periscope collider “exists” the edge, the “exit” event gets triggered.
You can see that if you pause the game and click the third button (not Play, not Pause) to flip through the frames.
Is this what you wanted to know?
See also:
- Forum User Guides : How to mark a topic as solved