The literal idea is of a formal procedure, like a trial in a court of law, or deliberations in a parliament, in which everything that says is being recorded. "For the record" means "someone has said something incorrect, and it is going into the official record. I don't want to let that go uncorrected in the official record, so, for the record, this is the correct statement." Informally, even when there is no real record, the phrase can mean "you're wrong, I am correcting you." There is a flavor of insincere apology. The person who says "for the record" is gleefully pointing out a small error. He wants to win a small victory in an argument. He pretending that it is important to correct the error, even though it is small, "for the record." In the dialog you quoted, it sounds as if Pierce is insulting Rockwell. He first corrects Pierce by saying the pirate was Algerian, not French. When he goes on to say "I can draw a map if it will help," he is pretending that Pierce made the mistake out of ignorance of geography. Algeria was a French colony until it became independent in 1962. There might be all kinds of cultural and political bias involved in mixing up "Algerian" and "French."

In politics, someone's nationality is not a minor thing.

If you say something 'for the record', you are making a statement officially and publicly which you want to be written down and remembered.

This is an example of subtext. "for the record" has 2 meanings. 1) to make sure the details of the conversation are correct 2) subtext: to show that you know something special about a situation Yen and Rockwell are mad at Pierce for letting a bad thing happen. They are trying to find out if Pierce is incompetent. When Pierce says "for the record, councilman, he's Algerian." he is trying to show that he knows something that Yen and Rockwell do not know. Yen and Rockwell are trying to find out if Pierce knows enough to do his job. Pierce is trying to show them that he is competent without actually saying, "Yen, Rockwell, I know a lot of things".

It is a way of emphasising the fact he is not French he is Algerian. By saying 'for the record he is Algerian' he is telling the person to hypothetically make a record of the fact that he is Algerian not French so he dosen't make or repeat that mistake again. If that makes sense!