Since he's so young the grip issues may or may not lead to anything, but if problems continue it could be a sign your child is disgraphic, a writing condition that can be caused by loose joints, weak muscles, and/or hand to brain issues. It is a relatively common co-morbid for children with ASD. The traditional pencil grip is literally painful for my son, now 21, and for that reason he never mastered it. The good news is that solid protocols for disgraphia have developed over the past decade and children who get help should eventually be able to communicate effectively and comfortably in writing.
But ... its too early to suggest this is a problem for your child. Just ... keep your eyes open as he matures and reaches the ages where unique grips leave the range of "normal." I'd say first or second grade should be when you will have a better idea.
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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).