It doesnt matter whether its true or not. The point is that at this moment of time it is the most plausible explanation, therefore for most of our intents and purposes it is "true" to us. You could say that it is a coherent truth beacause it fits in with most of the evidence we have availible.
------------------
These Ships among the stars serve as the physical embodiment of the God-Emperor's will, punishing all who dare oppose the doctrines of Terra