It's exactly that: just a web app

Most people can not differentiate between a web app in a browser and if an app they start through an icon on their computer is a wrapper around a website. People on HN who care if it’s built with Rust, Swift or an Electron app aren’t really the core audience for most companies.

It's even harder to classify as webapp if the app works offline, as electron apps often do.

Except that HN is exactly Fastmail's audience