Don’t scream and take a deep breath. It’s actual weirder to PDA with someone you’re not with that with someone you’re actually dating, even if it’s for some promotion, so I don’t see the logic either. If they didn’t PDA, they didn’t PDA that’s it. I don’t think they had some conversation before like “okay, I walk the red carpet, but not with you, we don’t touch each other, we don’t look at each other, but it’ll be clear enough that we are together”. Makes no sense to me.