So 4 people doing all the work by hand could do 500 bars a day. But now it takes 20,000 volunteers and they've made 68,000,000 bars, so only about 6 days worth of work per volunteer total?
Most volunteers are probably doing an hour or two at a time, and probably slower/worse than this guy's four close friends that were grinding through it. I would think some volunteers are doing other stuff as well.
The volunteers are usually half day corporate team building events. The company pays a fee and the staff provide "voluntary service", photos are then taken and shared on social media.