The reset button is basically just a signal to the CPU/BIOS that it should wipe memory and begin the boot process from scratch. If it was not working, that indicates the CPU was hard locked and not responding to any sort of input, not just an os fault The power button sends an actual trigger signal to the PSU through the ATX connector so it bypasses any mainboard lock.

Random shit happens, see if it does it again.
My go to for random stability issues is to always run a full deep memtest to look for bad RAM and then a CPU stress test to see if it’s a random thermal or core issue. More often than not I find stability problems just with these two steps.