The more apt analogy here would be if you had run your hose onto his property and left the spigot open, dumping unused water onto his lawn. All he's doing is visualizing images that are already being streamed to him unrequested. If he was bypassing some sort of filter then it would be stealing, but plugging the cable into the TV or running your hose over to his flowers instead of on his grass? I'm not sure labeling it as theft is really all that apt. I could see an argument for a moral issue here, but not really so far as theft. The proper course of action would be to inform the provider or in your analogy ask you to turn your spigot off.