I don't think the True Sith call themselves the True Sith.
Kreia spoke in riddles. She spoke in the terms "a certain point of view".
She implanted the idea that there is something worse out there, a boogieman.
I think Kreia knew if the Republic/Jedi knew there was no threat out there, which can not be measured, it creates a fear or wanting of preparedness. She wanted to make the Galaxy ready including the Jedi for a coming conflict even if it never happens.
Kreia saw the Jedi get comfortable. She will implant the idea of the True Sith who could keep everyone on their toes. Butů..
I do believe there is a True Sith. Kreia has been on MalachorV and studied the remains of this ancient Sith Empire. She still has not told the Exile all she knows. She knows that all you need to do is use the information you have to give the person a push in the direction she wants them to go. Kreia will release information to cement her ideas and suggestions.
The True Sith are a sect of Sith who are die hard in the ancient beliefs of the culture, a culture that was destroyed by the Jedi and the Republic along time ago.