[pnachbaur]

The article explicitly says "Characters with the same name can exist on different servers, so the mind-boggling 3.8 million unique names found in the dataset was not expected."

[MarkTanamil]

People don't choose a server so they can use the name they want.They play on the server their friends on (or chose a random one).

If the name isn't available they come up with a new name.