[yed]

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.

[terminalshort]

There absolutely are correct and incorrect ways of partitioning data into groups. Human genetics is no exception.

https://en.wikipedia.org/wiki/Cluster_analysis

https://en.wikipedia.org/wiki/Haplogroup

[yed]

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.