After using unionFind I am getting a cluster with 10k node

I used unionFind algo to divide my graph into clusters . I am getting many clusters but one of them looks weird since it has 10k nodes ( I have 40k nodes in total) !! Anyone has an explanation about that ?
I heard also about the "SUPER NODE" but I didn't find a tutorial/forums . It could be maybe the node which is related to 10k node is my super node ?