The only etiquette is to not leave hooks in/around their dock, don't be bouncing lures off their boat, and I won't fish one if someone is on it. Based on what you said you were in the right, and he was a bunghole. I would have politely told him you have every right to fish there and will be on your way shortly.
Nothing legally wrong and nothing ethically wrong IMO. I've run into it a few times growing up on a lake and fishing every rock that exists in it. Like others have said, I would'nt fish it if people were on it. Or wouldn't be bouncing lures off it or boats etc... Actually the reverse has happened to me with people fishing my dock. If I'm out and about I'll talk to them and ask them how it's going, tell them where I've been catching them etc... And for what it's worth I'd be willing to bet there is truth to this.
Ive been in the same situation. Fishing a public lake and went trolling back into a cove surrounded by very nice homes. This guy has signs ALL over his dock about how its private and do not fish near dock. LOL, we tossed anchor and proceeded to fish until the guy came out yelling and screaming, to which we politely waved, smiled, and continued to fish. When I fish docks I am very careful not to hit boats/dock with line. I dont get where this guy gets off claiming part of the lake like that.
