The queen is an expert at all this inspection of the troops and etiquette business, so to be generous you could say that Trump just turned the wrong way, was unsure or whatever.
However he has form, on his inauguration day I remember his leaping out of the car and up the steps, totally forgetting about Melania who was tottering on high heels holding on to a gift for Michelle Obama! President Obama was never anything but solicitous towards his wife.
Trump seems to be totally oblivious to anyone but himself.
He's a bully who likes to be in control, all that picking off fluff from Macron's jacket, bone-crunching handshakes, condescending hand-holding to put May in her place. He's truly unbelievable!