That's something I tried to showcase on the westside road barricade, a green sees you across a pit and has to bypass it to get to you. But there is a red here, he can't see you so he didn't attack but the fight between him and your new friend is inevitable, and unless you speedrun the game, you will just witness this event without taking part into it.
Hopefuly, players learn from those events before they actually confront the enemies.