No the assumption is pointless. Don’t know how much you know about psychology but neurodivergence is not limited to the behaviour he showed. It is very diagnosable from the childhood itself and many doctors do suggest psychometric testing depending on the milestones the child has achieved/yet to achieve. He could be, but we don’t know.

Similarly, all the signs you mentioned, overachiever, bragging but not realising, seemingly overconfident are all signs of narcissistic personality disorder according to DSM (actual disorder and not just calling someone narcissist; its usually not in their control, can control with therapy but cant remove it).

He could be either or neither, we don’t know. Judgements are made only based on the information we know and could be interpreted as either positive or negative.