The code is the programming, the underlying computer program which controls the game. While there are likely several programmers who contribute each game does tend to have a lead coder. Because the programmer is the one who implements all of the rules, scoring, etc he/she typically gets a lot of the credit. Most likely it a collaboration between the designer and their vision for the game and the coder with their implementation skills. A a key player in the team builing the pin certainly the coder does have the leway to add their personal touch as well.