1. It doesn't match the words. If that defines a "web app" then where does the web come in? I would think part of being a web app is that you can access it via the web and don't have to install it on your device.
2. Usefulness of the distinction to users. The specific nature of the bundled runtime for the code doesn't matter to anybody. It strikes me as pedantic to insist that because under the hood a thing is running in a browser we should call it a "web app".
I think the most practical distinction is that web apps have a URL as the entrypoint. If you want to use it, you can visit the URL from any browser that supports the app. Web app requires a URL and a compatible browser.
If instead you install the thing on your computer and run it from there, it's not a web app. It's a native app. No URL and it doesn't care what other browser you have installed because it comes with everything it needs. It's independent.
How and why would users be expected to understand anything else?