At nine months such behavior is just what babies do. No way to tell if yours is doing it more or differently than normal.
Infants have no social limitations and just do what feels good. And all sorts of odd things actually do feel good, even to NT's. As children grow, if they are NT, they stop doing them because they learn not to.
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Mom to an amazing young adult AS son, plus an also amazing non-AS daughter. Most likely part of the "Broader Autism Phenotype" (some traits).