They wont armwave at a human unless they think they are also humans , so if you have only one beardie who never sees another beardie , you''ll likely get some headnodding and armwaving.
I get headbobbing from my pet and resident wild skinks (bluetongues, water skinks, delicate brown garden skinks) very frequently, I interpret it as "hello nice human" , then tail wriggling starts (" I'm excitedly anticipating some of those yummy worms you give to me") , and the stare = begging for more yummy worms.
My beardies have headnodded at me (it's a different headnod to what I've seen given to other beardies). But not armwaved at me, at each other yes. I have been known to pretend to do beardie armwaves at my beardies when headnodding (at me), usually stops the headnodding and they respond with what I interpret as "what????" and the head cocked to one side.LOL .... my wife thinks I'm nuts too.