No way to tell at this point. Could be a bad bearing, could have had some fragment left over from a previous repair that got into the bearing and ruined it. They're not expensive, so, just get another, inspect the spindle and hub well, clean everything up, grease it good (and the outer bearing) and put it back together again. Since the outer bearing was ok (correct?) it's unlikely the nut was too tight. The outer bearing is usually the one to fail first when that happens, but, take care in tightening the nut. Personally, I don't put preload on the bearings. I find they last a lot longer (in fact, I've never had one fail that I've installed new) if you don't go any tighter on the nut than what you can do with your fingers. Just make sure everything is seated properly first. I mildly tighten the nut with channel locks or a crescent to make sure, and then back the nut off to finger tight.
