The thing is simple. Android app does not connect to remote databases directly. It uses HTTP requests as a middle layer of abstraction for communicating with anything including MySQL databases
So it doesn't matter what kind of server they have behind their API. They can use even text files, if they want. It doesn't matter to you. You just use their API.
You visit a store, you buy bread, you pay money, you get your bread. You don't need to know anything about how it is made, where it was made and so on, and it works here in the same exact manner