Oh no, they're definitely ASD. As I said, I work in ASD assessment so was confident about the diagnosis (which was made by a different team to the one I worked in just before they were 4 years old). It's difficult to fully capture how they presented as a toddler/young children in these messages. They are a fully rounded and complex individual, as we all are.
I definitely flip flopped in my thinking about the nature of their underlying difficulties from 18 months - about 2 and 1/2. Did they just need a bit of extra support or was it something more? And then things became clearer to me.
They did have all elements of the triad of impairment and it did affect their functioning in the world, particularly when they were younger. In assessment we look at the quality of communicative behaviours. So it's not necessarily whether a skill is present or not but rather the quality of it - how frequently or successfully it's used.
I guess my feeling is that my DC's autism doesn't define them but it's an important part of who they are. If I hadn't been a specialist professional, I probably wouldn't have picked it up so early but it would have been there all the same.
What you're doing for your DS is exactly what he needs. You're providing the communication environment to encourage his skills as much as possible. And it's paying off. Keep doing what you are doing. He is making progress and that is a positive indication for future prognosis. Autism or no autism, you are building his communication skills.