I am certain the American disgrace/former president, was invited by the Arkansas Symphony to do this as an effort on their part to fill more seats and sell more season tickets. Often, buying season tickets is the only way one can guarantee a seat at special performances such as this.
Why anyone would want to see him is another story altogether.
When I was a kid, I played in a youth orchestra. Bob Michael, who was Minority Leader of the House at that time came to narrate Carnival of the Animals for one of our performances.
This is all just a publicity thing for the orchestra.