This is no surprise, it's been established before that Daigo is a hothead, just now he was really interested in the case and some retarded villager grabbed his head to find out what he is doing. No way a hothead like him can keep calm. Plus it's never too late to just send your family back to Tokyo or wherever (we know that won't happen because the author needs to add drama, and what better and cheaper way of doing it than having a defenseless mother and defenseless child in a literal cannibal village).
I kind of expected this, and anyway the priest or the woman would have exposed it when asked by the villagers.
Actually if they (the villagers) were not retarded they should have figured it out as soon as the woman stepped out of the car.