The code is the computer code that runs the machine, written by a coder / programmer. Sometimes the programmer also designs the rules (as opposed to the designer who designs the physical machine), other times the designer also makes up the rules and the programmer just codes them (like elwin did for Iron Maiden). Lyman is one of the most respected coders, he does most of the rule/code design on his games and people tend to like them

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.