If asd is genetic, and it seems to be one of the causes, then certainly you can have one asd child after another. If you are asd yourself, chances are you won't notice. Then they go to school, where what just seemed to be your family idiosyncrasies get picked up as autism or adhd....
This.
We were told in DD1 asd assement that a lot of what we thought or is normal and is our wider family isn't in general population. We also often procorate with families who also turn out to have ND conditions in them and depsite some MN think generally we do well acadmcially and generally okay to good in life.
DD1 was pushed towards ASD by SEN and teachers and GPs - I never felt it fit but ASD assesor said many professionals don't know what conditions actually are let alone lay people. They then suggested dyslexia dyspraxia and inattentive adhd and yet more time later that was a yes to those after assesmnet processes
I think it's likely they've had cash for assesmenets - (we've had decades of delays and push back via NHS and cash for private a huge insurmountable stubling block for us ) but co-morbidity is so common - so ND is likely short hand for a range of conditions.
I do agree with PP though I've been more worried about trans pushing because my kids are ND - DD1 especially was at school in wales at it's height and it was hard to push back though depsite her ND trans friends she didn't go down that route.