Abnormal factory reset for samsung galaxy j1

A

AC Question

My girlfriend's husband's phone did an abnormal factory reset, he's got her old Samsung galaxy j1. It had died so he plugged it in when we got back to their place, it was only at 30% when he unplugged it. When he turned it on after unplugging it it was on the reset screen. Just wondering why it would do something like that.
Just for everybody's info she was able to remember her info so she was able to get it all straightened out.
Like I said we are just wondering why this would happen. If anyone can give me any knowledge on this it would be greatly appreciated.
Thank you very much and have a great day.