If I remember correctly, Electron was made for Atom (by GitHub).

Atom Shell, which was renamed to Electron, was made for Atom. Electron is not Atom. They both use javascript, too, but that doesn't mean they share code.

Yep https://www.electronjs.org/blog/electron

from the article "This is a tough goodbye. It’s worth reflecting that Atom has served as the foundation for the Electron framework, which paved the way for the creation of thousands of apps, including Microsoft Visual Studio Code, Slack, and our very own GitHub Desktop."

Yes. As the comment you’re replying to said, “Both using Electron does not mean they share a codebase, not in the normal sense of the phrase.” Code is no more a “rewrite of Atom that reuses a big chunk of the original codebase” than Slack is.

“both using Electron" refers to a period of time that occurs after "Atom has served as the foundation for the Electron" and my quote states that Atom -> Electron -> Spark

I'm not an expert on this at all, I'm just quoting, but Spark is being used rhetorically as if it's an outlandish to consider it to be a descendent