Yes, and no. They have a really interesting tale of convergent evolution.
Atom was the original Electron app (as pointed out Electron was even originally named "atom-shell"), so it predates VSCode as an Electron app. But the extremely performant "Monaco code editor" that VSCode was built on top of (that forms the heart of VSCode) was started at Microsoft years before to be a code editor in parts of the Azure Portal, and also it was the code editor in IE/Edge dev tools from as far back as IE 9 or 10 I think it was (up until the Chromium Edge). It wasn't packaged into an Electron app until after Atom, but it has an interesting heritage that predates Atom and was built for some of the same reasons that GitHub wanted to build Atom.
(ETA: Monaco's experience especially in IE Dev Tools and the wild west of minified JS dumps it had to work with from day one in that environment is where a lot of its performance came from that led VSCode to jumping Atom on performance out of the gate.)
Given GitHub's Code Spaces use VSCode rather than Atom, that writing is definitely on the wall, it seems. (Arguably the feature was built for Azure and then rehomed to GitHub where it seems to fit better, but still a stronger indicator brand-wise than most of the other comparative statistics in Atom versus VSCode commit histories and GitHub/Microsoft employee contributions there to, which also seem to indicate that Atom is in maintenance mode.)
Yes, and no. They have a really interesting tale of convergent evolution.
Atom was the original Electron app (as pointed out Electron was even originally named "atom-shell"), so it predates VSCode as an Electron app. But the extremely performant "Monaco code editor" that VSCode was built on top of (that forms the heart of VSCode) was started at Microsoft years before to be a code editor in parts of the Azure Portal, and also it was the code editor in IE/Edge dev tools from as far back as IE 9 or 10 I think it was (up until the Chromium Edge). It wasn't packaged into an Electron app until after Atom, but it has an interesting heritage that predates Atom and was built for some of the same reasons that GitHub wanted to build Atom.
(ETA: Monaco's experience especially in IE Dev Tools and the wild west of minified JS dumps it had to work with from day one in that environment is where a lot of its performance came from that led VSCode to jumping Atom on performance out of the gate.)