Loose water pump bolt

I was underneath applying fluid film since it was cleaned from the other day and I had nothing better to do. Anyways while I was underneath I looked up and seen a bolt not tightened down the whole way, maybe sticking out 1/4” or so. Im pretty sure it was one of the 10mm bolts to the water pump that came loose. The one above the crankshaft pulley and located on the inner corner of the water pump on the drivers side. I tightened it back up but I’m curious as to why this happened. There’s no signs of a leak nor any noise from any pulleys, it doesn’t overheat or use any anti-freeze, truck runs great, reservoir tank is still at the same spot from when i bought it. Anyone ever have this happen before or know why it came loose? Thanks

 

Has the pump ever been replaced that you know of?

 

Not that I’m aware of

 

Interesting I've never heard of one backing out, must have either gotten missed at the factory or the pump was replaced and it didn't get tightened.

 

That’s what I was hoping something simple as that, I plan on watching it to see if it comes back out again, truck just turned 96k the other day