I won’t even get into how you’re contradicting your first point about “strictest laws” and just quote from the first article.

It’s apparently spreading north as well – northeastern province Liaoning has been a “major growth area” for drug cases over the past few years, Ma said. Outside analysts believe that North Korea (which borders Liaoning) has become a major source of methamphetamine smuggled into China, although Beijing is reluctant to publicly point the finger at its ally.

So, not pot.