The point is there is no such thing as a “correct” grouping. The choice of what constitutes a group is completely subjective, it all depends on how far you choose to zoom in or out.
There are correct ways to group but there is no correct group size. Clustering algorithms inherently require some choice of sensitivity. There is no single correct choice for a given set of data, it all depends on what you’re trying to accomplish.
https://en.wikipedia.org/wiki/Cluster_analysis
https://en.wikipedia.org/wiki/Haplogroup