I can't read japanese, but we already know that files already copied to the Vita prior to the 1.80 update can work, if they use a 1.80 compatible exploit. So unless neur0n specifically stated that this is a new method to move files to the Vita, this Hello World could have been something he was working on as a backup or simultaneously with other exploits; i.e. there's still no way to hack your Vita if you updated and you weren't privy to the exploit game + had already installed the VHBL and homebrew prior to the update.
Hopefully he's found a way around this; just off the top of my head, I would assume that whatever checks the CMA is now using prevent a sufficiently powerful hack from using "files" that are simply data tacked onto the end of the required & expected SAVEDATA files? Otherwise it seems like the best bet is to somehow modify what data is about to be transferred after CMA has checked it and given the "ok" but prior to the actual transfer, although this is presumably too difficult without greater knowledge of CMA, or impossible if there are any checks VITA side or on each individual file as opposed to the folder as a whole.