For what I assume is a security precaution, SysRq is disabled by default in Fedora, and you need to go enable it if you want to be able to recover when shit like this happens - the link shows how, and explains what each letter does.
It’s honestly hard to say what caused it, but you could check your system logs and see what looks suspicious around the time of the crash. journalctl, dmesg and your steam logs (in ~/.steam/steam/logs usually) could be worth a look, or worth showing someone else at least if you aren’t sure whats going on in there.
I’d avoid actively trying to cause it, but if it happens again you handled it exactly how I’d try handle it. Having SysRq enabled would let r-e-i-s-u-b handle it more gracefully than a forced shutdown at least!