I would set the box up to syslog to see if someone is issuing the reload command. Also get a good handle on how many people have access to this box and if they have individual logins. Setup syslog and snmp traps to be collected.
But as for the reason, I recall seeing a box crash and said it was from reload, even though no one rebooted it. I'll have to look around more but I'm pretty sure you can see that in show ver and it not be a manual issue of "reload".
It couldn't hurt to also run your version of code through on CCO to see if there is a specific but you are running into. I'd also open a TAC case and if you are running older code, upgrade it.