The passive and simple past constructions in English are not exclusive. Clauses are considered to be simple past when there is one past tense verb and the clause lacks any marking for the continuous or the perfect aspects. The continuous is marked by the presence of the auxiliary BE and a gerund-participle form of the following verb (the -ing form). The perfect aspect is marked by the presence of the auxiliary HAVE plus a so-called past participle form of the lexical verb:
- The elephants ate the donuts. (past simple)
- The elephants were eating the donuts. (past continuous)
- The elephants had eaten the donuts. (past perfect)
Note that all three of the sentences above use past tense verbs, and that they only have one tensed verb per clause.
We can construct passive versions of any of the sentences above, and they will retain their tense and aspect labels. To do this we move the donuts to the Subject position and insert the passive auxiliary BE followed by a past participle form of ATE. Note that the passive auxiliary BE always comes last in the series of auxiliary verbs:
- The donuts were eaten. (past simple)
- The donuts were being eaten. (past continuous)
- The donuts had been eaten. (past perfect)
These three clauses all retain the necessary features for them to be labeled as past and then simple, continuous or perfect respectively.
The Original Poster's example
others were scattered in every pose of contorted collapse
How we analyse this clause depends on whether we view the word scattered as an instantiation of the verb or the adjective. The syntactic evidence here is largely inconclusive - although the meaning, given the surrounding paragraph, would suggest that it is an adjective (in other words, there is a reading where scattered indicates would indicate an event not a state, but given the surrounding description, this is not a likely reading). Either way, whether the verb scattered is a verb or an adjective , the clause is a past simple construction. It has one past tense verb, the verb were, and it lacks the necessary features to be considered either continuous or perfect. If the verb scattered is an adjective, then we would regard the clause as active. If it is a past participle form of a verb, then we would consider the clause as passive.