Conflicting meaning, between exam board / teaching resources, and technical meaning
You are seeing a difference between virtual memory as described to a computer user some number of years ago (this is more frequently called "swap" now), and virtual memory as understood by an operating system developer.

If one goes back and looks at, say... Mac OS System 7, one can see this description:


  Virtual memory adds more memory to your Macintosh by making use of unused free space on the hard drive. Because the extra memory comes from the hard drive, though, it is much slower than the RAM chips.


Or over in retro computing


  To avoid slow performance, Apple suggests that the amount of virtual memory you select be less than the system RAM.


This is the virtual memory as understood by a user.

Virtual memory as understood by a operating system designer and systems programmer deals with the virtual mapping of memory space used by a process to another space that is managed by the operating system.  It is not necessarily on a disk or any other medium.  It is not necessarily continuous in its physical addressing.