I don't see why my response is weird at all. I just disagree with you.
my view is that if a child is going to bring a toy to play group, they need to hold on to it, and if not, they need to accept that other children are going to want to play with it
Okay, and my view is that those 'other children' need to accept that not everything is theirs and they have to ask permission when something belongs to another child.
If it's a confusing concept for your kid at the moment that's fine, but that's what you're there for - to teach them, and reinforce it, not sit at the side with a cuppa or whatever it was you said. Most people send their children to playgroups and such to learn how to socialise with other children. At some point they are going to have to learn that sometimes things belong to others, and they don't have a right to everything just because it's in their space.
Your park / mobile phone example is odd - we're adults, so I'm not sure how it's relevant
It's relevant because it shows how we seem to expect children to readily give up (or "share") everything that's dear to them, while we wouldn't be comfortable sharing certain possessions of our own. I think children should be allowed to retain some choices in the way their belongings are used, and other children need to learn to graciously accept a "no".