The high pH in the UA can also be due to bacteria, and there were other abnormalities in the UA as well. The elevated WBC, Neutrophil, and CPK indicate infection although these tests aren't specific for what type of infection it might be. Even though there was no bacteria present in the initial UA, sometimes this can be misleading, and a culture and sensitivity should still be done to rule out a UTI.
If he's having diarrhea, the vet should get a stool sample and rule out GI infections as well.
http://www.merckvetmanual.com/pethe...bacteria_of_the_digestive_system_in_cats.html
Some of the GI infections can infect humans as well, so be careful handling his wastes.