It's not clear what happened here. Most rocketeers use "homemade" rockets in that they assemble kits; he could quite well have been using standard stuff with Estes (or Estivsky) engines. A rocket using those could kill you if they hit you in the head. I inadvertently used a one-size too big engine on a rocket I put together and it went horizontal immediately off the launch pad, about 5 feet off the ground. s**t happens.