They did the same thing for nearly 4 months with the ChatGPT desktop app, and it was literally just Electron. I think they just all use Macs and Windows is an afterthought.

I don't think they've ever released a Linux version of the ChatGPT Electron app and they said "Now available globally on macOS. Windows, iOS, and Android are coming soon" for this, so I wouldn't hold my breath for the Linux version of the browser either.

ChatGPT on macOS isn't built with Electron, at least the last time I checked. Just checking the linked frameworks shows that it links against macOS AppKit and the Swift libraries.

From a user perspective can definitely tell too, it's a polished, fast desktop app and has all the UI details one would expect from a native app.