Two SQL Server databases share the same MDF and LDF files but have different data
It is not possible to have two databases point to the same database files, except in the weird Autoclose case that you linked to, which no one should be using that setting anyway.

Run the below query to view what physical files the databases are pointing to:

SELECT database_id, name, physical_name 
FROM master.sys.master_files


With that information, you should be able to see that the databases are in fact not pointing to the same database files. 

You also can see this information in the SSMS GUI. Right click on the database, go to properties and then to Files. Now SCROLL to the right as the physical files aren't visible yet. The combination of Path and File Name will be unique.