It really did not go down well when my then 7yo (undiagnosed autistic) child was honest about describing another child.
The other child started with a factual but loaded observation about DS's hair, DS responded with a factual observation about the child's mass. DS got into further trouble because he couldn't appologise because a) the other child started it, and b) he was being truthful.
The follow up from me was explanation about how society values different observations differently and to not comment (so basically swerve the subject- which some would consider lying by omission) on peoples' size despite the "inconsistency" that other observations such as height are fair game.
Universal application of truth can be hurtful and achieve nothing positive.
In the news last night, there was a story about how the BBC need to withhold a report about an employee while the police investigate further. Releasing the BBC's truth at this point has the potential to bias legal processes.
The world is not black and white, it's a turbulent mass of grey.
Handling different opinions about Santa and Christmas celebrations is a fairly low-stakes way of children learning some discretion about how to work out fact/ fiction and truth.
A world of unfiltered truth would not be a utopia.
Diplomacy, creativity, fiction and a bit of "magic" make the world a much more pleasant place.