Should a child be required to share with other children?

So this mother took her son to the park with his toys and he had some boys come up to him demanding he share his toys with them, and this kids mom told them that he didn’t have to share his toys if he didn’t want to. Since the boy refused to give his toys to the other kids, they went to complain to their moms who gave the mom dirty looks. Was this mom in the wrong for telling her child that if he didn’t want to share HIS toys that he didn’t have to? Should parents be criticized for teaching their child to tell other children no and to not share if they don’t want to? My answer: no, it’s the child’s choice. But what’s yours?