Eh, not quite. I’d say a better analogy involves the posts being “I have a (insert car model here) and the brakes are making worrying squealing noises”, and “Hi, here’s a (link) to a trade-in offer for a model of car that’s much less likely to have the brakes fail on you. It won’t even cost you anything to swap except 30 minutes of your time.”
For me, a shutdown is when I stop cataloging the complex bits of what I’m perceiving and just go ‘listening to this is now unpleasant and I don’t want to subject myself to any more of this’. I might smile mechanically or emit encouraging ‘hmm’ noises, but I am on autopilot, you’re not going to be getting my higher brain functions applied to whatever you’re talking about, if I remember what you said it’s going to be as factual ‘this person said such and such’ memories instead of actual opinions on what you said, and I will dither on the far end of human interaction range trying to figure out if I can flee ‘right now’ without being impolite.
A meltdown… I get those, but I am experienced at calming myself down, so they’re basically ‘flashes’. Every so often, I will have a flash of… absolute, raging frustration at something. Like dropping my water bottle for the third time in a row after failing to pick it up twice. The first drop was an accident, they happen, they’re natural, I’m totally fine with that, I don’t even give it thought, I just go to pick it back up on reflex. Second drop, I’m like, oops, better actually give this attention, I’ll be more careful the third time. Third drop, my reaction is “REEEE I CAN’T PICK THIS THING UP! WHAT I JUST DID SHOULD HAVE PICKED IT UP! THIS SHOULD NOT BE!!!” And then I have to take in a deep breath through my nose and let it out slowly (and yes, I have surprised myself by actually making the ‘reeee’ sound effect while doing this) so that I can be PRECISE and DELIBERATE about picking the water bottle back up. This will then be followed by a temporary shutdown because I have just blown a fuse on my emotional centers.
The common point is, I feel, that they’re both reactions to something anathema, sort of. A shutdown is passive avoidance, a meltdown is active rejection.