I’ll check that out tomorrow. I didn’t look at the light when I was over there today. That would be funny if I could fix it. And he would never know I involved a bunch of people on the internet to solve his problem. 
I talked to his next door neighbor today and he said the old man is staying at his vacation home right now. The light fixture is a lantern type so we just took the top off and removed the light bulb. I’m not sure what kind of bulb it is but not a regular one. The glass is kind of dirty, so maybe it was reflecting the light back to the sensor. Anyway, problem solved for now. My neighbor said he would talk to the old man when he gets back. Thanks for everyone’s advice!
Oh, good. I am glad you found out what’s going on.