I've been an RO at 3 different ranges over the 30 years. Yes, you did something wrong, you crossed the line when the range was cold. No excuses are acceptable, especially from someone claiming to understand and practice proper "house rules".
The RO you dealt with was an ass from your point of view, (and all the sheep who've never heard a gun go off amongst a crowd on a cold line unintentionally will back you), but that doesn't excuse your behaviour either. My bet is the RO missed seeing you rack your rifle behind the line and only saw you place the ammo on the table. That set of circumstances, coupled with the fact that you didn't cop to handling *something* on the table, escalated the entire incident into an 'argument'. Your description says the RO was "some distance away" when he hollered at you while you were at the table. (How 'action-opened' guns are handled from vehicle-to-rack during a cease-fire is a variable according to "house rules". At two of the ranges I RO'd, handling *any* iron was taboo during the cold period; at the 3rd range, the only entrance to the line funneled past the RO's best vantage point, and he could stop all incoming folks with a quick, "please wait here until" the line turned hot.)
If the shooting line is long, there's no way to see everything on the tables down the line; it's like standing obliquely next to a cyclone fence and trying to look through it; thick glasses or not (and you can belittle his eyesight as much as you please) he saw you cross the line, and made the worst assumption possible, which as an RO is the best assumption to make, at any distance. I thought he handled it well, waiting until the line was hot, to speak to you "privately", until you 'mutually' got out of hand. If my description of his impressions are correct, I lay no fault *whatsoever* on the RO. You better believe, I'd raise my voice and threaten to drop kick *anyone* out the door immediately if they stand and argue their safety conduct was proper, if their reason doesn't jibe with what I think I saw ("I was never handling a weapon with people downrange") --all you had to do was state that you'd racked your rifle and brainfarted your way to the table with ammo only, and I'm sure the whole situation would have diffused itself.
I'm glad not to have to screw around anymore with the obstinant idiots and self-righteous experts handling guns among strangers and neophytes. There's enough of them out there that a whole weekend didn't go by when we'd have to listen to "attitude" while performing this volunteer duty of keeping an assemblage of randomly gathered experts and neophytes safe during every minute of their (sub)conscious range use.
I'm sooo glad I don't have to use supervised ranges.
I shoot on my own property now, and the unknown quantity of a stranger with a gun on the firing line doesn't even enter into my shooting scenarios anymore. God is good.