[x86 hardware]
---[Slashtop Linux Kernel]
------[apps]
OR
---[Some (any) operating system]
------[apps]
Basically, it's an alternative OS to boot on the hardware that comes pre-installed on the motherboards (I assume on some built-in flash memory, doubt it'd be on ROM). Don't be confused by the 'VM' in the 'DeviceVM' name (not sure if they have anything to do with Virtual Machines at all).
The idea is that instead of spending time to boot up the normal operating system on the computer, you can very quickly boot into a minimal Linux OS to accomplish some tasks... although with Suspend/Hibernate becoming pretty standard I'm not sure how useful it would really be in practice (MattPerry's post lists a couple advantages to it, although I'd more so list those in the utility category).
They refer to this "custom, in-house-designed real-time operating system (RTOS)", which I'm now guessing is just a modified linux kernel - probably with proprietary binary drivers bundled with it.
The article says that the RTOS is not linux based, but I'm starting to think that is a misinterpretation.