Honestly I would not jump straight to dairy issue. I feel like everyone is always screaming dairy issue (fwiw I do have a child with a legitimate dairy issue and he never has bloody stools) . If it is a 1 time occurrence I would not worry, however of it happens again I would go get it checked or at least talk to the dr or nurse and if the green poo and blood continues explore the possibility of a dairy issue.
The only time you should look in your neighbor's bowl is to make sure that they have enough. You don't look in your neighbor's bowl to see if you have as much as them.