I think one difference is that it also provides the service of being a production environment you can serve from at the same time as development. There's more information about this thought in the fly io blog post.
The linked fly.io article discusses why containers aren't a good fit for sandboxes that need persistent state and how sprites.dev addresses the challenges.
I think there are tradeoffs here. Maybe your one person vibe coded app doesn't need any change management, IaC, any of that. No docker file, start with whatever docker file fly wrote for you, beat it with an agent until it works enough. And it's pretty cool that you can then just serve it directly. Is it dev or prod? Yes.
On the other hand, I really don't think editing php files over ftp in prod was ahead of it's time -- I was there, man, and it sucked. I just know I'll be really confused about why something doesn't work eventually and wish I had some tracking of what changed over time. I want my IDE. I want VCS!