The issue is that drugs tend to be available and encouraged for rockers and actors.
Heroin, in particular, seems to have an unnatural appeal to guitarists and rockers and has claimed way more than it's fair share of them.
I really wish we would legalize some of these drugs even if we still keep them behind a prescription. Legalizing the drugs would certainly help as then the dosages would be controlled.
I think (without bothering to do any research to source my claim beyond my personal experience as a paramedic, and the sources available in the article) that the widespread availability of Naloxone (and other harm reduction based policies) are far more likely to be the cause of the decrease.
I'd guess it's a combination of many different factors.