How to describe cluster center?

Hello Gromacs users,

I do not understand how to describe cluster center generated by gmx cluster via gromos method.
On gromacs website, center of a cluster is defined as the structure with the smallest rmsd to other structures in the cluster. I do not understand this.
Should it not be the structure within the cluster that has the smallest and most common rmsd to all other structures in that cluster?

Many thanks,