The article has the title it has because they couldn’t conclude otherwise. JAMA wouldn’t let them get away with it.
“Legalizing Medical Marijuana May Reduce Opioid Deaths”
Where is it written that titles are always identical to conclusions (or lack thereof)? "In the years after the legalization of medical marijuana, states that did so had a rate that was 25% lower than what we’d expect to see in that state, given past trends and what was going on in the rest of the country" is a conclusion, while not being a practical title (nor a proof of cause and effect).