This is just my attempt to understand it, but I think a "meltdown" is usually a reaction to a sensory overload, when something just becomes too much to handle. If that's the case, melting down is not really just an autistic thing; it's a human thing-- it's just that aspies and autistics tend to be more sensitive to things that neurotypicals might not even notice, and are thus more likely to get totally overwhelmed and "melt down."
I think that different people react to overload in different ways, too. It's been a long time since I melted down in a way that caused a scene (such as a lot of crying), but that's because I tend to deal with the possibility of overload by hiding, whether that means literally finding a place to be by myself, or by retreating within myself and trying to shut everything out.
I'm no expert though, so this is just speculation.