Makes sense. That tends to happen after you try to do something positive and reach someone. It's happened to me a lot after sharing my faith with others. A thought to encourage you is that attacks come for a reason. They are designed to discourage you and stop you from being productive. They can make you second guess and doubt yourself. If you are getting attacked it's because you are doing something right
It sounds like you handled the situation well. I wouldn't worry about trying to disprove Islam or try to pick apart his beliefs ( not saying you did). I'd concentrate more on pointing him towards Christ. He's going to be won and affected by his opinion of you and the truth about Christ that you shared.