You must be seeing something that I can't see. The hand on the forearm? Mehh no big deal.
Macron walks right past Trump who is ready to shake hands. Then he shakes hands with several other leaders, his back to Trump. Then he turns around and acts like he might walk past Trump. Trump then smiles and offers his hand, but not far from his body, as if half expecting Macron to ignore him again. But, Macron not only takes the hand, he appears to be going for some sort of finger crushing handshake there. Something is up with the braced, two handed technique.