There is a wire that I think is a ground of some type? I have it too, it runs from the distributor to the passengers side, iirc, and grounds out. I was kinda curious about that too when I changed my plug wires.

 

I saw it, but didn't say anything because he stated that it is running fine now, so with that said I assume that he put a tune up on it after finding the wire is missing, however did not state that. IMHO...I think that was a mechanic verbal oversight and did not mean that he did not fix it.