genuine question please dont flame me

[myplateisfullenoughthanks]

No offence intended.

Could fantasising/compulsive lying be considered an autistic trait?

Not a parent of child with ASD.

I would have thought not. Normally from reading these boards and friends who are parents of children with ASD it seems to be the opposite. i.e. literal thinking and inability to lie.

This illustrates the autistic spectrum quite well but does not mention the traits you enquired about.
theaspergian.com/2019/05/04/its-a-spectrum-doesnt-mean-what-you-think/

Fantasising/compulsive lying is surely psych/MH based, not autism. That's not to say an individual could not have psych AND MH difficulties AND autism.

It can not infrequently be part of a PDA presentation which is part of the ASC spectrum. We were actually advised to keep records in case of any serious accusation (luckily this has not happened).

There is a myth that people with ASC do not lie but this is certainly not true for my two but no more than most people I would imagine.

I think it is more that people with ASC think that when you ask "does my bum look big in this" you want the honest answer.