Ok, I understand. However, not to get TOO technical.. but in your example, the appropriate gesture would have been an open hand outstretched, palm facing upward, followed by a slight, sweeping movement in the direction of the person he is introducing. Extending one's hand, pinky-finger-down and thumb-up, is nothing but an invitation for a handshake. I can think of no other possible use for a hand gesture such as that. In addition, look at his facial expressions, as each (hypothetical) offer for a handshake is denied. You can see that he is troubled by it but trying to keep himself together. The 3rd person he comes across he doesn't even extend his hand toward because as I hypothesize, he figured it out and didn't want to endure the embarassment of a 3rd denial.
I hope you don't think I'm being petty. I actually get what you are saying but the way the hand is held would tell the story. Also, can you see where Obama said, as you contend, "And this is Mr. So-and-So?" If he says nothing at all, it leans again in the direction of handshake invitation.
This is actually kind of a fun sidebar debate. I wish others would join in.
Humphreys? Your opinion?
Every one who is seriously involved in the pursuit of science becomes convinced that a spirit is manifest in the laws of the Universe-a spirit vastly superior to that of man. - Albert Einstein