Flaxseed I did research into Autism at the Institute of Psychiatry, not all that long ago. I had to assess and diagnose Autism. So, please believe me, your delightful DGS is too young to assess. It is true that retrospectively parents of Autistic children do report a high number of "good" babies.
However, this is not a red flag and many babies who do not develop Autism are contented, easy-going and uncomplaining, like your DGS.
My middle daughter has 4 children, the 4th is amazingly easy-going. He didn't complain about anything as a baby. No. 3 as a toddler, amused us by doing so many weird things but also had marked speech delay. We were quietly watching in case any more "Autistic" signs appeared. I have Autistic relatives. DGS3 seems fine and dandy. No 4 is now a toddler and the two of them are a big handful getting up to all sorts of pranks.
My DD no3 has a second child, now 1yr old, who was also a baby who never complained, slept like a log where ever you put him and was just so easy it made you feel guilty! I shall have a word with him about this when he's older as his mum gave me a terrible time when she was a baby and I thought that at last she would find out what it was like... (She's one of those people for whom everything always goes perfectly so she thinks it must be my fault if she cried as a baby for example.)
I expect you can see where I'm going... Please stop watching and worrying over your lovely DGS and try to simply enjoy him! None of us has a crystal ball, so don't spoil today imagining bad things about tomorrow. Just let him be himself and love him for it. Let each day take care of itself.
Wishing you good luck with CBT, it's great stuff!