Use the MChat test to see whether he might be at risk of autism. My feeling is that he will pass the test, but do it anyway. When answering yes or no at the test, think of it more as mostlly/rarely , not as pure yes/no.
Keep on mind that if he does the following, then it is a high chance he has nothing to do with autism:
point to objects to attract your attention, bring you toys or books to play with, responds 40% of the time to his name, has an appropriate eye contact, plays peekaboo by pulling blanket over his face, is fine to play side to side with other kids (not yet with with other kids as he is young for that) , looks at you sometimes from across the room (2meters plus distance, for example) to see that you approve of his actions or just to see you, and if he smiles at you then he definitely doesn’t have autism, when you smile at him few times he mostly smiles back, if he is repetitive or obsessive about something you can fairly easily interrupt him (let’s say my boy spins the wheels a lot but we can always sit next to him, start playing with the ball or something else he likes and he comes to us within a minute).
Autism is about a cluster of red flags, not just one or two of weird behaviours because toddlers up to 3 years old tend to exhibit some autistic traits without ever being autistic. Just because your child is awesome with numbers and counting also doesn’t mean he is autistic. There are kids out there being number savants just by the way their brain works.
If we are to assume the worst and say, he has autism with SPD, his autism would be so high functioning, he could be one of those adults later on in the life who diagnose themselves with autism when that are over 30, married, with a full time job. The impact of autism on someone’s life is directly correlated to the social and communication skills until the age of 2.
This being said, I do think there is a sensory issue with him. These issues are fixable to the degree and also, as the brain matures, some of the sensory issues will disappear. Not that it means you shouldn’t work with him.
I am not a medical professional, but I know a lot about the autism because my boy failed mchat test with 8 red flags 4 months ago. We started speech therapy as he has language delay, I’ve been obsessively reading medical articles about therapies and autism. Our son is now down to 2 red flags, some behaviours corrected with our hard work. He still exhibits some autistic traits but at 16 months old, there is still chance he will be improve by bounds. He is a typical sensory seeker and if si coming with sensory seeking to get strange reactions from their brains, either overactive brains like your son, or a language delay like ours.
Hope this brings you closer to the solution.