Well, that parent will probably do this, every year.
Helicoptering their child and deciding who their child plays with.
Unless your child is a Bully, then this is probably just an icky parent who is super picky about who child their child plays with.
Parents, try all kinds of things or complain about all kinds of things. Even if it seems silly to others.
To them, THEY want what they want.
A parent, also has a responsibility, to teach their own child, about people and how to speak up, and how to choose friends and what to do to discern other kids.
Growing up, kids make all kinds of friends and those friends have parents that "we" may not like personally or have the same lifestyles that we prefer. But so, again, a parent has to teach their child about life and about different people good or bad, and teach them how to choose friends or not.
Its just life.
Is this YOUR child, that the parent is saying to separate and not be allowed to play with your child? Or is it another kid but you are curious about it?
What is a 'negative' influence to one parent, may not be to another.
it is real subjective.
I always teach my kids, that everyone is different. BUT, if a kid is inappropriate or a Bully or a bad personality, then they go and play with someone else. I teach them how to 'Discern' other kids.
A Teacher, cannot just make kids not play with a certain other kid. That would be or can be construed as that child being ostracized or targeted or singled-out. Then what will the other kids, think of that kid? It is a real ripple effect.
And, where does it end?