No, there is no rule that you always have to use the passive form.
However, I realized that a Japanese sentence often omits the subject, often implying the subject is the speaker without other context, and that this style makes the sentence in the passive form.
He told me what I needed to know.
can be translated to
(Disclaimer: I am a native Japanese speaker, but not an expert of language)
I feel there is a slight difference in meaning between (a) and (b).
Sentence (a) is the natural choice in most cases because of the relative-tense rule you have described. But (b) may be used to describe certain situations:
Other people ...
This is a kind of rhetoric device called historical present. It's also found in English novels and news headlines, but typical Japanese novels use it extensively.
Why did the author briefly jump to present tense in this article?
Negative present endings translated as past tense
i am confusesd as to what historical present tense is, when it is used, etc