I'm sure someone here (Adrianus?) can give you a good reference for Latin grammatical terms--after all, we have the words of plenty Latin grammarians from various eras.
I think Orberg is relying on unstated nouns, here.
"Plusquamperfectum passivi [verbi] constat ex participio perfecti [verbi] et praeterito imperfecto verbi 'esse'."
"The pluperfect of a passive [verb] consists of the participle of the perfect [verb] and the past imperfect of the verb 'esse.'"
I don't see a problem with the way you did it. It's a question of whether to use the adjectives as adjectives, or to use them substantively. "Plusquamperfectum passivum," "participio perfecto," and "praeterito imperfecti verbi" all make sense to me. But perhaps this violates a precept of Latin style of which I'm unaware...
Horae quidem cedunt et dies et menses et anni, nec praeteritum tempus umquam revertitur nec quid sequatur sciri potest. Quod cuique temporis ad vivendum datur, eo debet esse contentus. --Cicero, De Senectute