I wonder if heroin is still obtainable there, unlike in the US where the only option is a bag of fentanyl cut with whatever the favorite local garbage substitue is. That alone would go a long way toward the differences in OD rates.
I have heard anecdotally that Europe still gets lots of heroin (someone in a similar thread recently said opium poppies come to the EU through Turkish black market trade). No clue how true this is.
It stands to reason that people cultivating opium poppies didn't throw up their hands in despair and decide to do something else with their lives when Chinese fentanyl (which is made in a lab without any opium) started taking over in the US. The opium is going to go somewhere.
In any case, an article using overdose death as the primary metric for success/failure of drug policy should not be ignoring the dramatic difference in fatalities between fentanyl and other opiates.