This eruption happened in the 16th century BCE, so Plato was writing about it over 1000 years after it happened. I’m skeptical a story can be passed down that long through oral tradition without changes, so no surprise all the details don’t match up. I would even venture to say that since the focus of this discussion is “something someone once wrote down” and keeping in mind that “people can write down anything they want to” I would say it was completely invented as a thought experiment.

But I’ll also take that Plato could have used an existing folk tale describing that very event as the basis for a point he was trying to make. Especially if his audience was already familiar with said folk tale.