He would probably still be alive if the physician wasn't using a quack method for treating autism. The article says that EDTA is FDA approved for acute toxicity of PROVEN heavy metal toxicity. I'd bet that the child did NOT have any lab work proving elevated levels of a particular heavy metal.
You're absolutely right. Both of the doctors mentioned in the article are MDs and could've easily ordered lab tests to check for heavy metal toxicity. I suspect that most autistic children don't really have high levels of heavy metals to detect in a blood test and that these doctors use chelation regardless of what blood tests would indicate.