Agree with NH that I hope you didn't pay for it! But onto the more important part -his health. He ate, so I would be encouraged. Barring a regurge, he will almost certainly live. And he hides, which is what snakes do, so behavior is normal. I hope your temps are perfect, because it is important anyway, but paramount for a weak animal. I would feed every time he defecated for a couple of months, at least. For what it's worth, being a yearling, at least it has some body mass. Do you have any photos? Can you get a weight in grams? Sounds like you are off to a good start. Be sure and keep a clean dish of water at all times. Dehydration can be a killer, especially since the snake is already compromised from a lack of fat storage. A yearling snake should be on much larger food items than pinkies, but we will need to know the size to determine that.