Pedantic, but VS Code does not share a lineage with Atom, besides the fact that it is built on Electron (which was, admittedly, originally built for Atom.)
EGreg didn't mean to say that VS Code used to be Atom, or is based on Atom, though I agree his wording was a bit ambiguous and it could be interpreted that way.
During that time, Atom was released (2014). But I don't recall it ever being especially popular - at least outside of the JS ecosystem. For one thing, it was kind of slow on release (people still complain about Electron!) and while it offered a lot of customization, these customization often seemed to worsen its performance. It was VS Code that really seemed to draw a wider audience from my perspective.
That said, I switched to vim around the time Atom came out, so I may be out of touch. I doubt there are any solid stats anywhere...