Biketiger

I am biking along a paved multi-use trail today and I see a rider coming towards me in the opposite lane. About 10 yards away he raises his right arm skyward. Clearly he is signaling a turn but I am confused as to which way. I'm thinking maybe he wants to go left which would cross my path but still at a safe distance. He turns to his right.
I appreciate his use of signals (most people don't) but I was really confused about the straight up arm. If he wanted to go right, why not just stick his arm out to the right? A signal anyone could accurately interpret.
It took me a minute to consider that while driving an automobile without a turn signal, the driver could stick out their left arm signaling a left hand turn but you can't point to the right so the raised arm is used instead.
But on a bike?
I did a little research and the League of American Bicylists recommends either method. From their site:
"Right Turn: Fully extend your right arm out to the side or bend your left arm up at a right angle with your hand flat."
That advice makes no sense to me. If I am making a left hand turn in front of you (assuming a safe distance) I will point left.
If I am going to the right, I'll point right. This straight up business defines ambiguity.
What do you think?