This is the typical trade tactic for rejecting a job that is too small to be worth your time. He still has to come out to your place, with his truck and tools, and install that 8 feet of cable. He could spend that same overhead doing an 8 hour, much more profitable job.

So he bid an outrageous amount. If you had said yes, he covers his overhead. If you reject it, he does something more profitable with his time.