It's part of the Intent system in Android. It's a really nice system where you can say "someone open the file with this URL and mime type" and the system asks the user which app they want to use to open it (or use their default if they set one.
It all works really well and lets app be loosely coupled to each other. It's also super flexible so you can use it for lots of different use cases. The API itself hasn't changed much since the first release of Android.
The issue is that you can query the Intent system to see if there is an app installed that can open your Intent. On the face of it, this makes a lot of sense. You could then display an error message to the user asking them to install and app that can handle it. The problem is that you can create an Intent that you know can only be handled by a single app (using the package name) and then you'll know if it's installed or not.
For what it's worth, iOS used to have exactly the same issue. You could query the phone could handle a specific "custom protocol scheme" (used for deep linking). You could then just query a scheme which you know is for a specific app and tell if the user had it installed. Apple fixed this by requireing you to include a predefined list of schemes which you can query for in your Info.plist (manifest file) and limiting the number you can have (30 I believe).
All APIs with good intentions, but very easy to abuse. Apple is just more comfortable breaking backward compatibility to fix these sorts of issues.
