I have just had a good read of their website and they really do not seem to want to shock and annoy people. It makes an interesting read actually.
There is an intro before you scroll down : "This site provides information about the World Naked Bike Ride in London. If you continue you will see some non-sexual images of naked bike riders. It is a popular, peaceful, legal, public protest on the streets of London but parental guidance is advised to ensure the beneficial intent of the ride is understood and well received."
There are numerous references to sexual behaviour and arousal not being tolerated, careful sensitive instructions about getting dressed quickly at the end point, not spending time walking around naked, etc. They don't approve skateboarders, scooters etc on the ride, because of the increased 'visual exposure'