Wasn't Electron created for Atom? If so, VSCode is at least using a part of Atom.

That doesn't make Electron _a part_ of Atom. If I build my application on top of Linux, my application is not _a part_ of Linux.

Electron is its own application framework, that Atom builds itself on top of. Electron is not a text editor framework, no more than QT or Cocoa is.

It is _very_ fair to say VSCode is using Electron - heavily, in fact! But saying VSCode is using part of Atom is just not true, and implies VSCode is building atop the Atom editor, which it does not.

I mean, by that argument Windows uses Unix because C was written for Unix.

At least historically Windows used different parts of UNIX. i.e. they used BSD's TCP/IP stack for quite some time. Also used "UNIX services for Windows" and recently added the Windows subsystem for Linux.