Google "autism denial" and you'll see there are a lot of parents of ASD kids being told by well-meaning if ill-informed friends and family that their children are just "going through a phase." To those people I'd just like to say, autism is not a phase. Sure, it's possible with help and time the ASD child may improve. Or they may get worse. I guess in that sense autism has its phases.
But autism is a lifelong condition, not a fleeting trait. It is how the brain is wired, and it informs the very nature of the autistic individual.
It's not just being shy or awkward or unique. Autism doesn't just refer to children incapable of communication. And it doesn't mean the ASD child can't be bright or happy or even funny, nor does it mean they will be a Rainman-like savant.
In fact, it is often said there are as many forms of autism as there are people with autism. I suppose this is true, but across the spectrum there are common, detectable traits that define the condition, regardless of any individual's unique personality.
I think it's worth noting that friends and family who suggest "it's not autism" mostly do so from a place of love; they have good intentions. They don't want to believe it to be true. What they may not realize is that by denying the diagnosis, they are undermining the very people they love.
Imagine if you had cancer, but everyone you loved told you it was probably something else...indigestion or stress or poor sleep habits. How would that make you feel? It would be downright maddening.
No one wants to accept the autism diagnosis, least of all the parents whose child has been so diagnosed. But once that truth has been accepted by the parents, friends and family would do best to get on board, or keep their opinions to themselves.