I configured the new phone (Samsung) to my dad and he wanted the freebitco.in shortcut in Home and that was the only way to let it put in the Homepage, I never saw it by the way and I trusted the procedure. It doesn't seem to download anything, it seems like some sort of wrapper of the website, but in the previous phone (Xiaomi) he owned, there wasn't such a feature, it just placed a shortcut to the browser Chrome.
It seems legit by the way, but I'm curious to know more.
Most probably it's the browser/ site behavior which can be seen on more recent versions. I use Brave browser and occasionally some sites will have a script which sends a prompt for the user to save it on the home screen, with personalized messages.
Not really.
It is initiated by web page. They prepared "manifest" file:
https://freebitco.in/manifest.json which defines icons and label for proposed link.
Then that file is served to client with that piece of code in the page source:
<link rel="manifest" href="https://freebitco.in/manifest.json">
All together causes mobile browser to propose link creation.
Behavior is described here:
https://developer.mozilla.org/en-US/docs/Web/Progressive_web_apps/Add_to_home_screen