Hello, Aine here, one of the etke.cc developers.

The stats of the matrixrooms.info instance is what matrixrooms.info instance sees - it is not whole Matrix Federation. Here is the documentation in the MRS repo about that endpoint: https://github.com/etkecc/mrs/blob/main/docs/stats.md

Also, at the moment of writing, there are ~15k *federated* online servers visible by matrixrooms.info, and from them, ~4k servers publish their rooms directories over federation ("indexable").

You can read more about the MRS project (matrixrooms.info is just a demo instance) in the repo: https://github.com/etkecc/mrs/blob/main/README.md