Yet everyone on Ashli’s side of the window yelled “gun, gun, gun” before she attempted to climb through.
There was chaos on Ashli’s side of the doors...it is just as likely that the yelling of “gun, gun, gun” caused Byrd to exit his hidey hole and cap Ashli - the coward could have taken the yelling as referring to Ashli, not himself. While he was lying in wait, he was not visible to those on Ashli’s side of the doors