And infinitely lower reliability because you can't have failovers (well you can, but people that run everything in the same host, won't). It's fine for something non critical, but I wouldn't do it with anything that pays the bills.
Random guess, a php error caused Apache to log a ridiculous number of errors to /var/log and on this system that isn’t its own partition so /var filled up crashing MySQL. The user wiped /var/log to free up space.
That's not far off of something that happened to me once a few years ago. My computer suddenly started struggling one day, and I quickly figured out that my hard drive suddenly had 500 gigs or so of extra data somewhere. I had to find a tool that would let me see how much space a given folder was taking up, and eventually I found an absolutely HUMONGOUS error log file. After I cleared it out, the file rapidly filled up again when I used a program I'd been using all the time. I think it was Minecraft or something. Anyway, my duck tape solution was to just make that log file read-only, since the error in question didn't actually affect anything else.
I'm not sure what the future of MariaDB is... It lacks a bunch of newer MySQL features, and they've deviated far enough that I don't know if they can cleanly backport them from MySQL any more.
Like everytime with natives, it was a race condition cascade of table locks followed by mysql suicide caused by bad cronjob scripts implemented by the user.