Facebook mbasic site, mobile safari, home screen shortcuts and local storage

I have a question about the mbasic.facebook.com page and how they manage to do what they do on iPhone with iOS 12.3.1. This is not about the facebook app. I don't have it installed at all.

I went to mbasic.facebook.com in mobile safari on iOS and created a shortcut for it on my homescreen. When I use the shortcut, the page behaves like what Apple calls a web application, i.e. it does not have the usual mobile safari UI.

Here's the weird part:

After using the shortcut and logging in, I switch to the settings app and under "Safari", I delete the browser history and website data.

I then use the shortcut again to launch the mbasic facebook site.

I am greeted with a screen where I still appear to be logged in. If i interact with the page it will make me login again, however.

This makes me wonder about two things:

1. How does the web application maintain its state (i.e. still know who am i) despite me trying to delete the Safari data?

2. How do I delete the data in a way that also affects a "web app" launched via a home screen shortcut?

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