I'll speak for me here, not the OP. I find that many ranges, particularly near the Big City where I live, don't allow anywhere near the degree of freedom that some of the other posters mention...meaning, most ranges around here would feel "uptight" to those folks.
I also think the RO may have been being kind and, as I might, the OP took the constructive criticism as a personal attack. As someone already said, the environment around some ranges seems more hostile than if you were at a book store, Wal-Mart, etc. I still remember being rebuked for saying "45 APC" instead of "45 ACP" and having been condescended to in the explanation....more than 25 years ago in my then-LGS. Some people can be testy, and my level of insecurity can exacerbate that. I now stick to LGS' without a high quantity of SWAT/Special Ops wannabees behind the counter.
Lastly, judging from some of the folks that come in and out of the skeet club I belong to, I can see why ROs assume you're dangerous until they get to know you. The safest position to take is to assume the new shooter has either never had safety training, or has been trained badly.
I would have had a similar reaction to Atom's, I would have made the same "mistakes" (the gun case one seems over the top), and I would have also reacted poorly to the coaching.
Down the line, you may find the RO is a great guy who is hyper-cautious.