The NOUNLOAD option is for restoring from tape, and this example is restoring from a disk source.

I found the example code a little confusing because of that option. It's not clear why it's there, and according to the docs the option is simply ignored in this case.

Referencing this MS Docs article:

RESTORE Statements - Arguments (Transact-SQL)

Which states:

{ UNLOAD | NOUNLOAD }
Supported by: RESTORE, RESTORE FILELISTONLY, RESTORE HEADERONLY, RESTORE LABELONLY, RESTORE REWINDONLY, and RESTORE VERIFYONLY.

These options are used only for TAPE devices. If a non-tape device is being used, these options are ignored.