If he is copying ALL the .mdf and .ldf files, AND SQL Server is NOT running while th copy occurs, then this is a form of relatively safe backup, but its certainly not recomended, nor a very usable way of backing up the system.
For example, its the most expensive way to do a backup as you have to stopthe server, AND copy ALL Db files to ensure a consistent backup. If the server is running, OR any DB files are NOT copied then any attempts to restore the system from files copied while SQL is running, OR if any DB files are missing may result in an inconsistent DB thats effectively worthless.
The safest way to do the backups is to use the built in SQL server backup options.
Co Author "Professional SQL Server 2005 Administration"