Hm, I think it is probably a bit more nuanced than that. Sure, insecurity with rejection plays a huge role. So does having having a brain that orders information in a neurodivergent way, be it more jumbled up, associative or more structured.

I often need to know everything about a certain topic until I feel like I understand it. And it has to follow logic. If you only give me single bits, I will be confused. So when explaining stuff to other people, I try to convey as much information as I can because that's what I would need as well. This might easily be confused with mansplaining or with being pedantic. I point out logical fallacies when I spot them because my brain gets confused otherwise. Some people might also misread this as power play. But usually my insecurity speaks for itself I guess because if you are outwardly insecure it will fail as power play (e.g. mansplaining).

Another aspect of neurodivergent oversharing is getting obsessed with a special interest that then everything revolves around and you want to only talk about this topic. I guess it is a state where the brain is so focused on this one thing that the outside world just isn't as relevant. This might also be confused with mansplaining, but is probably more likely to be read as socially awkward? Although both have in common that the other person is seen as somewhat irrelevant and unknowing.