It is based on the Linux kernel + your application. So an ultra lightweight image indeed. The advantage is that all components are rock solid and standard.
Thats not technically a unikernel, unless you link them into a single executable (which has licensing issues with Linux). Single application OS would be a better term, as it is confusing otherwise.
Linux... Buried in there:
> Congratulations! You now a have a brand new 54 MB secure unikernel image including only our application, Java 8 and the Linux kernel!
If you have a separate runtime & kernel, is it still a unikernel?
Yeah, this appears to be a bit misleading. It sounds as if they're just running the compiled jar as the /sbin/init process. IMO, thats a very lightweight distro but not a unikernel. #NotAnExpert.