OKay, registered nurse here. Mucus indicates irritation in the bowel. I would say that is due to some sort of parasite. Drinking from standing water (puddles) is a great way to pick up parasites, especially in a country where hygiene standards are not as good as they are here. Parasites DO NOT always show up in the blood. The vet needs to do a fecal flotation. If he can't do that, even examining a sample of the poop under the microscope will spot many common parasites.
Second most likely cause of the mucus: an infection in the bowel, which antibiotics can fix.
As for feeding bones, anyone who feeds raw knows too much bone causes CONSTIPATION, and hard, dry, whitish stools with undigested bits of bone in them! Look it up: there's lots of info out there on raw feeding!
When I was a kid, I was told to never, ever feed raw bird bones. Bird bones are hollow inside, and that means when they are broken, they have very sharp edges that can puncture the gut. Some tribes of native people actually used to make arrow points out of bird bones before they were able to get metal from the Europeans. And now all of a sudden, we are feeding RAW CHICKEN to our pets?? What changed??
Ask any vet out there: they will tell you how many times they have had a dog or a cat with a bone trapped in its mouth, teeth, throat or gut, and the animal needed treatment to have it removed. It's an everyday thing for them. Oh yeah...I used to work for a vet, so have seen it firsthand.
Lastly, most chickens we eat in N. America are very young, and the bones are still immature and very soft, and not likely to cause trouble. Cooking softens them further, especially pressure cooking. So, things are different here than they may be in the Philippines.
I think the owner is wise to cook the chicken. Raw chicken is a major source of a number of nasty bacteria: salmonella, E. coli, and C. jejuni especially. I got the last one from some undercooked chicken in a restaurant meal, and it totally ruined my vacation in England. Some people say dogs are immune to whatever might be in the raw meat, but why take the chance?