Shit is brown because red-blood cells are constantly recycled and replaced and they come out in your poo. He had to shit out his old dead blood at some point.
To be fair, a new born baby has a full digestive tract. They have been 'eating' and 'defecating' during the last leg of the pregnancy while in the womb. That stuff has to empties out of their system when they are born.
I feel like a 2 year old asking this, but, "He defaecated infrequently, roughly every 40 to 50 days."
How does that work if he wasn't eating any food?