If anything this shows how pangram is unreliable. Chances are, if someone is running an article generation thing, it'll be 100% generated. Writing 3 / 100 articles "by hand" doesn't make any sense.
But indeed, if Pangram is marketing itself as "near-zero false-positives" now, that entails that the are aggressively biasing it towards being conservative, likely leading to lots of false-negatives and low match scores on AI content.