There's different teams doing different types of work.

Like the claim system might have it setup so X codes in Y situations can't be automated. Then someone looks at the claim, determines based on their written guidelines that this one needs to be reviewed so they look to see if there are notes attached. If there aren't they request the notes, maybe by sending a letter. If there are, they send it to the team that reviews notes and makes these decisions. Those people probably also have written guidelines on what is allowed or not and if it's more complicated they (should) have someone qualified that can review it. Then the claim is probably sent back to the other team saying "Hey, deny that code and allow this code", where they then just do whatever that says.

They probably also have situations where X code in Y situation is "never" allowed and the first people reviewing it just always deny it. Then, as mentioned elsewhere here, the provider has to resubmit it and then it's allowed on "appeal" by another team. This brother you mentioned is probably doing very little decision making beyond applying already decided guidelines to each claim, if he even processes them.