He was a new mafia player so I assumed he was attempting to role-play and chose a character from the film.
Thatguy used to sometimes drop his role at the beginning of a game -and it would typically end up bad for him- but he is an experienced player. He was shooting the moon and is one of the few players that could possibly pull it off.
For fun, I'd give my role publicly sometimes. Sometimes I'd lie and claim I'm mafia publicly. I think I claimed to be the killer once, too. It would work in some cases. In others, it wouldn't.
There was one game where I tried saying everything the opposite of what I meant. That resulted in me confessing I was mafia in the thread, and saying I wanted to be voted out. As it was happening, I proclaimed that the people playing the game were very smart and making the best moves possible. I died shortly after. I'm not sure if any players caught onto what I was doing, but it was a little fun while it lasted.