belt tensioner too tight?

[FlyingRed]

I just experienced a catastrophic failure of the bearings in my waterpump. They completely gave out without warning to the extent that the pulley started grinding into the pump housing. (The impeller even scored the block)

Since this seems to be a strange failure mode for a waterpump, I'm trying to decide if anything else could have caused the failure. Could a belt tensioner fail in such a way as to have too much tension on the belt? (I'm always used to hearing them get too weak) The truck only has 95k miles on it.