That was I thought, but I was not! Here is what happened:
1 - I picked the left door
2 - Monty opened the right door
3 - He does not offered me to change (so, the door I chose was the green door)
4 - I open and it was red
So my interpretation is :
1 - Monty chooses a door (1/3 chance)
2 - If player chooses this door, the mechanism works
3 - If the player does NOT choose this door AND Monty opens the choosen door, the mechanism could not apply
4 - So, the player still have 1/2 chance to get the green door
I'm not telling it's bad idea, it's totally fine following the Monty Hall problem as well, but for a jam game it's really too random and frustrating.