It looks webview-based, but otherwise it's a native app.
No, Typora is an Electron application, occupying more than 200MBs on disk (and similar amount of RAM upon start with no documents opened). See this announcement for example: https://support.typora.io/What%27s-New-0.9.66/
Maybe you're both right. That announcement implies it is only Electron on Windows/Linux.