You were tuned into the tunnel, as I explained in my post (sorta

). I'll go into detail here.
You were tuned mostly into the tunnels since that's where you expected the guards to come from, as I said in the post you were the first to notice and turned around first, but you were too late. It's a fairly long tunnel, but you're able to see the entrance to the...what was it 30' room?...from where you stood, by the time you senced them, turned around and you had a chance to react there were 10 arrowheads pointed at you.
Ok? Well even if it isn't that's ok because I'm technically running the show. I tried to be as fair as possible, and I just gave you a chance to get out of it, but I'm counting on this to move the story along. So there you have it.
Curse you stumble button!