[Ephedrine]

his head moved. or least thats what they wanted us to believe that he saw.

my guess is that he set the trap in the hopes that a dark seeker would think it to be human, but in his state he forgot all about it and become trapped himself, and the dark seekers showed up due to the blood he dripped.........

I agree. You could have seen him set the trap earlier in the movie, when he throws the rope up to the bridge and makes a loop in the other end. ( I been a boy scout, I knew what he was doing lol )...