My bachelor male GT behaved similarly. He would court any large moving object, including my finger. It's not an aggressive glass banging action, but head shaking courtship movement. The one in the video has passed on, but his bachelor son is doing the same thing, courting a vieja melanuras. My fish friend told me that his male GT would court a convict. So the odd behavior may not be odd for GTs. I have no other breeding CAs in the tank, so I don't know if he would kidpnap someone's fry and gruard them as his own.
[video=youtube;lfV8f0-G_z4]http://www.youtube.com/watch?feature=player_embedded&v=lfV8f0-G_z4[/video]
Your male definitely has a 'finger fettish'.
This is one species that has more than its fair share of character. They're a 'strange' bunch.