Let me slide into my Cal Lightman mode here. It's not merely a politeness hug because you need to feel comfortable to put bare hands on someone's bare back and squeeze. There's pressure but it looks like light pressure, which says consideration. It's a formal occasion after all. The left hand is low already, which is also indicating they're both comfortable with that, but notice how his left hand isn't putting pressure on her at all. It really looks like a compromise between a squishy hug and a red carpet hug that gazillion people are going to see. Also, his smile is real, not fake. I suppose her hands are sort of trapped between them and I'm not sure what to make of it, since I can't see her face, but going by her posture and shoulders, I think she's feeling comfortable as well.