She never outright stated that Nihilus is the way he is because of that technique, only that it's how he harnessed the hunger he gained.
This is further revealed when the Exile can reply with 'But those Sith on the Harbinger were quite weak' or a random version of that line.
If she was referring to Nihilus himself I'd agree, but she isn't, in-fact when you ask her about the 'Lord of Hunger' she never makes any reference to the Ancient Sith whatsoever and calls him an Echo of Malachor V, clearly he's a special case that only happened due to his emotional state and lack of force sensitivity beforehand.
But regardless, I don't want to hijack your thread.
Don't worry about it, I would agree with you here. I doubt Nihilus has any real knowledge of the ancient technique, it all seems very instinctive. Nonetheless, from what Kreia says it must have some links, I agree that is very far off from what happened on Nathema though.
What did you think of Darth Vacuous (AKA DS Meetra) do you think she's a character worth exploring?