First it shows how the top CTFs can showcase the state of the art in terms of exploitation. It's hard for anyone to argue that the CTF scene does not reflect the "real world" when it is producing solid work like unpublished virtual machine escapes. And even better, the work is shared in high quality writeups.
Secondly, this plus other vulnerabilities found in VirtualBox emphasises that off-the-shelf hypervisors cannot be considered to create a security boundary. Every serious nationstate possess weaponised exploits to break out of VirtualBox, VMware etc. KVM and Xen have a smaller attack surface and are known to have a better isolation model, but I'm sure there are still plenty of exploits given enough resources. Perhaps this is obvious to some, but some people really do think that VirtualBox VMs act like a sandbox, which is only true if your adversary is rather unsophisticated.
For a writeup from the same CTF, but focussing on networking and cryptography instead involving an exploit in a Chinese anti-censorship proxy tunnel, please see https://blog.cryptohack.org/cracking-chinese-proxy-realworld...