This is running Linux binaries on Oracle Solaris (which they call SmartOS), and not the real thing that Oracle is still developing, but a fork from 2010 that is maintained by 1/10th of the developers it once had. https://www.openhub.net/p/illumos.
This would have been pretty rad 10 years ago, when the world still cared about Solaris.
On a minor note: the post doesn't credit Oracle or Solaris, from where more than 90% of their SmartOS code comes from, until Oracle closed their code in 2010.