The vehicle was not speeding or driving recklessly. It had no broken lights or expired tags, nor had the car been reported stolen. What it did have was out-of-state plates on a rental car.
This is enough to trigger a traffic stop during Operation Rolling Thunder, the annual five-day law enforcement blitz that turns a 20-mile stretch of freeway between Charlotte, North Carolina, and Atlanta, Georgia, into a gauntlet for travelers.
This in itself is illegal.