> Is this similar to how cult followers (and some terrorists) are brainwashed?

Not exactly.

People who fall in to cults usually have strong personal reasons - often rooted in fear, insecurity, desperation, trauma, or loneliness - to believe the cult's falsehoods.

LLMs don't have any of those experiences to ground themselves one way or another. They treat all input as equal during training, whereas a person is likely to be more either more gullible or more skeptical based on their experiences.