Am I bad parent for not knowings my son’s interests?

His 3.5 ASD level 2 and I still don’t know his interests..I wish I knew exactly so I can get those things so he can dive in and learn. His into his train toy, says choo (rarely). (attempts) to say shark, like watching that animal video where they name it and drop it in the bucket of water (replays the shark part a lot). He hates reading books. But likes coloring. Just a bit of everything….i thought ASD kids were reallly into something and your able to tell right away.

Or what age do ASD kids start showing interests…

What things can I try or do that will tell me exactly the things he need🙏