They are different things. A meltdown is a neurological event, in which the brain isn’t operating in the same way and higher order thinking and reason are inaccessible to the person.
However, I guess it can be hard to differentiate as an observer.
i grew up with an angry shouty parent, not ND in the way you mean here but had a brain injury, which technically is neurodivergence. Also an alcoholic. Volatile and unpredictable. That parent has died now but I never felt safe or comfortable around them, and it directly caused a lot of psychological issues in myself and my sibling.
My other parent, I think is likely autistic, although I think they themselves would disagree. I am diagnosed AuDHD, all my dc autistic and all but one ADHD. So strong genetic element.
I have understood this parent’s behaviour differently since seeing it through an ND lens. They were a generally loving parent who would on occasion lash out verbally and physically, completely lose it. With hindsight, I think probably meltdown due to overload. Reached a point where they melted down and completely lost it.
I can understand it in relation to my own experience of meltdown. Which is that if i don’t pace input, or if I’m not left alone to regulate when needed, I will inevitably lose the plot and be completely unable to control it. Knowing I am ND, and knowing what I need, has allowed me to avoid it. It’s vanishingly rare for me to get to that point, but I live a life that allows me not to. My parent wouldn’t have had that understanding and possibly not had that luxury. I know that they tried hard and loved us.
Not sure whether this goes any way to answering your question, OP, but it’s my experience.