Hola Wylie

Don't worry about the typos...

So, do you mean that the past perfect in English (e.g. had opened) could be the tense used in English as the equivalent of the Spanish preterite (Pretérito Indefinido, e.g. abrió)? 

Well, it is not exactly the same, because we do have the equivalent of the English past perfect tense which is the Pluscuamperfecto (e.g. había abierto). With the sentence you gave us:

"I surveyed the room. The teacher had opened the door." 

we can be literal on this in Spanish and say:

"Inspeccioné la habitación. El profesor había abierto la puerta." 

here there is an action that happened after another. First, the teacher had opened the door, then I surveyed the room. This is a specific usage of the Pluperfect/Past perfect tense.

The usage that we explain in the lesson about the Pretérito Indefinido (the preterite) we see an action that "happened" and we see it as something that had a beginning and an end. The action is completed. 

Fui al trabajo. = I went to work. ( I did that action, I am not walking to work anymore, because I finished the action of going to work, if this makes sense.)

Hice la cena. = I cooked dinner. (I did that action, I am not cooking it any more. That is a completed action.)

And we compare these sort of examples with the Imperfect (in the lesson) where, despite being also a past action, we see the actions as something "happening" in the past, without seeing them as completed:  (Iba al trabajo / Hacía la cena)

Saludos

Inma