Absolutely it could be a parasite. They're highly transmittable. Try an OTC wormer, but if it doesn't clear up in a week and a bit, he'll need specific shots from the vet.
Otherwise, there are products that were recalled recently, but 9lives wet isn't one of them. It's been a while, so if the bags are fairly recent, that shouldn't be an issue.
I recently adopted a kitten from a shelter and he has had diarrhea. He is not gaining much weight, though he eats constantly. Now my other cats have the diarrhea too, and one showed some blood in his stool. The stool is not watery, just very loose. I feed them a high quality dry food and on an occassion I will split a can of 9Lives moist food between them all. This is strictly a treat, not a main staple. Could this be worms or giardiasis? Bad canned food? Or worse? Thanks!
It could be a parasitical infection or an IBS condition. Try a diet geared towards easy to digest foods and worm the cat.