Blood in the urine sounds like a urinary infection. It really good be anything-I'm not too sure if Kibbles n Bits would cause that. I knew a dog on Gravy Train his whole life and he's still kickin at 17 with no problems other than being blind and somewhat arthritic. If the dog's straining to pee, if very well may be kidney stones-it's very heartbreaking to see.

How old is Nebo? It could just be he couldnt hold it. Maybe some slight bladder weakness. At least he was trying to get outside. If it continues, or worsens or anything you might want to talk to your vet.