What a false positive is
A false positive is a piece of human writing scored as machine-generated. It is not a near miss or a low-confidence reading; it is the tool asserting something about authorship that is untrue.
False negatives get discussed less and matter just as much: generated text scored as human, which is now common enough that a detector's clean result on a suspicious document tells you very little.
Both errors come from the same place. Detectors estimate whether text looks statistically typical of model output. That is a guess about style, and style overlaps between people and models for entirely innocent reasons.
The consequence is asymmetric. A false negative embarrasses a detector. A false positive can fail a student, damage a professional reputation or end a contract, which is why the standard of evidence should be much higher than a percentage.