OK, I've look it up in Alexander Souter's A Glossary of Later Latin to 600 AD. There's about 1 1/3 columns of words beginnig in pseudo-, e.g., pseudoapostolus 'false apostle' to pseudothyrum 'false (secret) door'. Name that keeps cropping up is [Sophronius Eusebius] Hier[onymus] aka Jerome, he of the Vulgate. So, it became a kind of prefix with the Church Fathers.

Ceci n'est pas un seing.