The Clark County coroner ruled that Dave Dave died in July of sepsis, due to pneumonia.
The Las Vegas artist was 42 years old when he died July 15.
Dave was a close friend of Michael Jackson. Jackson met him after the boy, then known as David Rothenberg, survived a 1983 attack that left him with burns over 90 percent of his body.
His father lit the boy's kerosene-soaked bed at a Southern California motel during a bitter custody battle.
The Associated Press contributed to this report.