They're referring to the Windows kernel; see the preceding paragraph on the Windows kernel - the three general purpose OS families are Linux, macOS, Windows.

Personally I think not enough credit to macOS here; Apple's Mach/XNU has been microkernel flavored since the NeXT days and many subsystems run in userspace like Windows.

Last years Crowdstrike outage never hit any of the macOS computers with CS installed because on macOS the Crowdstrike agent runs entirely in userspace thanks to the Endpoint Security framework.

Really the security of macOS is probably the best of all of the desktop OSes, and as annoying as it can be.