I don't think it qualifies as a twist. A twist in movies for example, is when you think someone was a good guy the whole movie until the end where you discover they are the opposite of what you thought, and you say "Whoah!" in your best Keanu Reeves voice.

There's no "whoah" here. Nothing significant has changed. An extra detective? SHOCKING

This changes everything! Now that there are two detectives...well wait they only investigated 2 people per turn...so it's just like one detective...except they can identify the Godfather. Woo.