Can’t it be both? I’d you truly believe the earth is flat because the person who taught you geography purposely led you to believe so, isn’t that both a sincere belief and a lie?
Yes, since the definition of 'lie' covers both intentional and unintentional deception, but I interpreted the above comment to be referring to intentional lies. " Maybe she figured out that making up bullshit gave her power" doesn't read as sincere belief to me.
Using the definition of “lie” that includes unintentional false statements sort of dilutes it to be meaningless. It means everyone is a habitual liar (“you said it was 23C when it’s actually 23.5C you bald-faced liar!”).