This condition validates the value returned by @SERVERNAME against the SERVERPROPERTY('MachineName') and SERVEPROPERTY('InstanceName') values and evaluates to True when it does not match the expected value.
This can have rammifications for Always On Availability Group backup processes that make use of the sys.fn_hadr_backup_is_preferrred_replica() function where it will return a 0 for all values passed to it when the @SERVERNAME value is incorrect. This has been raised as a bug with Microsoft via Connect and details can be found here.