I revise my earlier statement about what happened. It's possible you were a prick, but my guess is neither you nor the UA pilot knew about the flowback process specifics and were using the 'classic' rules of jumpseating.

He should have had his credentials ready to go and still asked rather than tell.

You will know better in the future if this happens again, he was technically correct because he checked in with you so calling him back up was in hind sight a dick move.

Anyway I wouldn't feel too bad if I were you. Neither of you were totally correct. You get my respect for asking about it and being open to dialogue.