From the email title, you can see that there is a bit of snickering on the part of the email originator on what these Cambodians did. Now, my guess is that there was once a Cambodian lad who probably was fascinated with rockets. After successfully building his first one, he started to build them bigger and bigger. Then, he discovered that if he put several rockets together on a wheel, they would not rise so fast. However, the wheel started slowly for several hundred feet creating a beautiful swirling exhaust cloud.
From the video, it seems that this is a community event. Everybody in the town or village came out to watch and enjoy. I suspect this event had religious significance. As you may know, Asians near and far believe that fireworks chase the spirits away. I think this a clever endeavor in mixing religion and fun. You can laugh at the guys as crude rocketeers, but they probably had fun building it and fun launching it to scare the evil spirits away.