Past perfect doesn't necessarily have to refer to two actions, but rather can compare to an action (in the past) which is completed prior to some other (past) point in time which can be specified but also which can be implied. See:
past per·fect /ˈˌpast ˈpərfəkt/ adjective
1. (of a tense) denoting an action completed prior to some past point of time specified or implied, formed in English by had and the past
participle, as in he had gone by then. - Google
Look at the example sentence above, "he had gone by then." - there is no specific other action in that sentence, but clearly one is implied.
That is why the sentence you give may be correct, because in context of surrounding sentences there may be another past event which is implied in this sentence, and the reason for using the past perfect form is to show that these events are being compared.