Well, Bob, since you are known to have "the personality, patients, demeanor and calm of a Saint", not to mention always being mistaken for Brad Pit, wherever you tread, (or, so this is what you keep telling me, so it's obviously true....), I can't, figure either, what you may have done wrong!?
Except, you did mention something along the lines of...."I reentered the stream, 15 to 20 feet below him". That, actually, if one IS fishing a particular lie, is only half the normal casting range, for your average stream. So perhaps entering so close to him, he figured you'd ruined his spot!?!
An old rule of thumb, for stream etiquette, is; "To enter and leave the stream, around another fisherman, at least the distance .... of being no closer than the average flyfisher can easily cast".
(Of course, now with Spey casting is becoming so popular, THAT particular rule is going to require one to buy airfare and dig out their passport).
Oh! You, didn't perhaps, forget and wear your; "I Share My Pillows With A Lawyer", ball cap, did you? Some guys are really, really, touchy about such things ya' know!?!
But, I agree with the other posts too...................it sounds, in all probability, that the man was just a complete and total jerk. There's no reason, to go on and on about someone else's mistake, if made innocently, let alone, get so angry about it!
If this jerk had calmly and quietly, explained his upset to you, it would have been the correct way in my book, to settle the whole thing.
Who knows, Bob? Maybe he was just having a really, really, bad day. Maybe, YOU were the perfect ruse for him to use as an excuse for his lack of skills and fish catching abilities? Maybe, before you, he'd ran into Mediclimber, spoke to him and was feeling really, really, inferior about his personal liquor supply?