AITA for tipping on amount, and not percentage?

I (33M, working in corporate, I was on a business trip) recently had a one on one client diner in NYC. We went to some nice, fine-dining restaurant. I spent roughly 650 dollars on us two. I tipped 50 dollars. After the client has left (I was still sitting there, I was texting my boss) the waiter asked me if something was wrong with the service. I said that it was great, to which he responded by asking if there was a reason why i you tipped him so little. I said that I gave him 50 dollars, which I found rather generous Anyways. He then went on to explain how the tipping system works. I asked him, that well, what difference in his work does it make if I order a 5 dollar burger or a 200 dollar steak? He carries the same plate, same route, etc. I asked him would he treat me differently if he knew from the start. He didn’t answer. I refused to tip more and left. AITA? Or maybe I don’t understand the American tipping system, as I am a Pole and it was my first experience of fine dining in the USA?