This isn't so much a range question as it is a question of how to communicate effectively.
The RO acted like an idiot, unfortunately. If he had a problem with you he should have told you specifically and precisely what the problem was. ROs should not be the least bit vague, they have a duty to the other shooters to be specific and accurate, and above all non emotional. Given the fact that you were/are not aware of what his specific problem with you was, then he did not communicate effectively and left you not knowing what exactly not to do in the future - hence he is an idiot and did not perform his duty. Did you do something wrong? Who knows? If he caouldn't or wouldn't explain it clearly then how could anyone know? On the other hand, you could and should have communicated better by calmly getting him to be specific.
Two rules for arguing with idiots:
1. Never argue with an idiot because he will drag you down to his level and beat you with experience.
2. Never argue with an idiot because bystanders won't be able to tell who is the idiot and who is not.
In the future, remain calm, do not become argumentative, defuse the others persons emtional/agression by your utter calmness and sincerety. Ask specific questions, and keep asking them until you get specific answers that you understand and that make sense to you. When you think you know what it is he is trying to say, repeat it back to him as in "Oh, so you mean that in the future I should leave my rifle in my vehicle until...." and he will either confirm that you do now understand, or clarify in more depth.
Confrontations with idiots occur everywhere, not just on the range. It is unfortunate though that the range let anyone act in a responsible position like that without some form of training.