The full context of the paragraph, which is important here:

A virtual machine boots a guest operating system. Raven instead implements Windows interfaces through these guest components and supervisor services. Wine also implements Windows interfaces; the distinction here is how Raven divides that work and supervises the guest, rather than whether system libraries exist inside the application’s process.

I’m not entirely understanding this, but it sounds like a hybrid concept between WINE and a virtual machine. So its only partially virtualized.