Like the hint suggests, I am not writing a single line of GDScript in the solution video. I'll change the phrasing if it can help.
It may be a difference of what you consider "writing" vs what a noobie like me does. If I am typing, then I am "writing."
The hint was about writing lines of code, not just writing. Anyway, I changed it already.
I shall add that the hint make me choose a "less code as possible solution" too.
The previous lessons make me think that the StompDetector was a element (ie a functionality) of the object the player can stomp on and not a functionality of the player itself.
So I have duplicated the enemy scene, only removed its scripts (because it was managing its movement), kept its StompDetector and changed the detection layers to make my bumper works.
But I must admit that I have some difficulties to adjust the different collision layers and masks between kinematicBody2D and Area2D to avoid my player being killed by the bumper. I have some docs to read to understand this mechanism
It can actually be written without writing any new code because EnemyDetector just works as it is (only need to add necessary masks), but separating things here is a good practice because we don't want, say, a coin to kill a player on collision because it also relies on enemy code.
I didn't use or modified any code as Nathan implies the only thing that I changed is that the bumper is a StaticBody2D instead of KinematicBody2D. The mask of the bumper itself is Player, Enemy and World. That way when the enemy collides with it it bounces back and the player doesn't die since it's not a KinematicBody2D. That's the solution that I found.