I find it misleading to call this section "Past Perfect." Germanic and Romance languages have past perfect (or pluperfect) tenses (https://en.wikipedia.org/wiki/Pluperfect: "In Polish there is no pluperfect except of texts written in or imitating Old Polish, when it was formed with past (perfect) tense of być "to be" and past participle of the main verb."). Polish AFAIK contrasts perfective and imperfective verbs (https://en.wikibooks.org/wiki/Polish/Verbs: "The Polish past perfective doesn't have anything to do with the English perfect tense - it's used for completed actions and is more similar to the English simple past."). It's just a matter of terminology, but I think it would be less confusing to learners if you used the term "past perfective."
But this is course of Polish not English. And "Past Perfect" refers to the Polish tense which can correspond to English Past Perfect, Past Simple or Present Perfect.
Yes, this is a course on Polish not English, so why use a term for an English tense that doesn't exist in modern Polish? Why not use "perfective"?
You shouldn't identify "Past Perfect" as "Pluperfect". Neither it means that Polish Past Perfect corresponds to English Past Perfect. It can correspond to it as well but not exclusively.