I don't understand the whole "Flame throwing guitar player" meme from the movie. What does that mean? Is it a reference to something or some other movie? I don't get it.
I think they were trying to hit on two things with this.
The first being a kind of battle call. Instead of using something lame like a trumpet why not an over the top guitar playing guy hanging off the front of a truck? It's suppose to keep the battle energy high and intense.
The second is, it's an attempt to show his status as a leader. Extravagant display of power having a huge stack of speakers while a guy jams away. For a post apocalyptic scene it would be very excessive. You would have to have a lot of things taken care of to pull that off in a wasteland.