Errors of interpretation, for one. When my students read Chaucer and think that the knight being described as "meek as a maid" means meek as a servant (instead of a young girl), they have not made an error in fact, but one of interpretation.
Errors of interpretation or understanding (see almost any layman's explanation of the Schroedinger's Cat thought-experiment as evidence) are not as egregious as errors of fact. A layman might easily miss the significance of a detail that might mean much more to a specialist, but to get a basic (and easily verifiable) fact wrong shows a carelessness that is much worse...
You make a good point, but the FACT of what was written was true.
What was 'interpreted' was a FICTION in the readers mind.