What does it mean If a guy takes a picture with his arms around you and he clinches his fists, is that a sign they are just friends?

My ex took graduation pictures with this one guy and in every photo he has his hands clinched when putting his hands over her shoulder. I assume that couples or people who are physically comfortable would wrap their hands around you with their palms.

What does it say?
What does it mean If a guy takes a picture with his arms around you and he clinches his fists, is that a sign they are just friends?
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