It's normal, this message just means your mentor has different incarnations (= different characters that belong to the same progenitor).
As an apprentice, you can speak to any of them : the message will be redirected to the proper character logged in.
Don't worry, it's still the same person/account, it's just to make it easier for you to communicate with your mentor so you can always reach him, even when he's logged in another character
Cheers, have fun !