The answer is not the same in all places, but here is the general idea: Traditionally (going back to medieval England), a coroner is a king's representative who looks into suspicious deaths. ("Coroner" is a corruption of "crowner", a person who represents the crown = king.)
In the U.S., a coroner was typically a person with no medical training who was elected to sit as a sort of judge at an inquiry into a suspicious death (a coroner's inquest).
In modern times, many political jurisdictions decided they wanted an expert to decide why people died. They hired a person who was usually called a medical examiner to do this. Medical examiners are physicians trained in post-mortem examinations.
Some jurisdictions have only a coroner, some have only a medical examiner, and some have both. The news media have no clue what the difference is, and even if they do, they may choose to ignore it to make the story sound more interesting.
To get down to your question: If the "coroner" was truly a coroner, he or she was elected, and training was not a part of the job description. If the person was a medical examiner, it should have been someone with an M.D. and specialized training on top of that.