Yes, it's so interesting how sometimes the entire sentence in Polish sounds exactly like Russian or vice versa. Я Русский если что)
Może być also means 'maybe' 'perhaps' and the translation as " It might not be the truth" should surely also be acceptable-może być?
Here, the negated word is "może". So it really has to mean "cannot". For your sentence, you'd have to negate "być". "To może nie być prawda".