Seems like it's more the awkward person doesn't want to presume the person has given them permission of physical contact for a quick picture and they opt to do hoverhand
I mean I understand if you're going to grab someone by the hips or waist, but the shoulders shouldnt be a problem for anyone (unless you're sweting or something).
I understand is a different culture, In South America everyone from the opposite sex will greet you with a kiss in the cheek, and a little hug even bosses, doctors, teachers, or anyone unless its something extremely formal, so a hand in the shoulder its like nothing.
I'm traveling to Europe by the end of the month for the first time, so this is kind of important to understand for me lol.