Pure speculation on my part, but a guy outside could have pushed the coax through the gable vent with one of those long extendable sticks the VDV folks are so fond of. If he just went to the attic opening and retrieved the end, he might have never seen the fan at all.
I was thinking cable guy with a temp helper of the "beginning ESL" variety. Cable guy pushes cable through from the outside, helper doesn't say anything (doesn't speak much English to start with) because: 1) He assumes Cable Guy knows what he's doing, and 2) He doesn't want to contradict they guy who's paying him.