Yup, the CLOSE_GROUP is a data-ownership concept, but not used at all in the shunning process.
Nodes close to, can and will judge neighbours. They may inform them of that decision (I think that’s the you have been shunned
type log we’re seeing… ). That means that one node has shunned it. That is. currently permanent for that node. But if no one else shuns, you’re still sufficiently in the network.
So effective shunning is an emergent behavior, rather than one that requires consensus or some threshold.