Halo CE: Anniversary campaign glitch

Hi i just started replaying the campaign from halo after getting frustrated at the online matchmaking. On mission 5 on halo CE the game out of nowhere, for no apparent reason, switched to the original halo graphics, guns, scenery, covenant etc… It doesnt sound like a big deal but there is a HUGE difference between the remastered and the original. I tried restarting, reloading and wont go back to the remastered. Anybody else have this issue?

Hit the “back” button. It switches the graphics instantly.