North Korea's actions are contrary to the theory of being China's puppet. North Korea does rely heavily on China for trade, but that doesn't necessarily translate to political influence. In fact, North Korea knows better than anyone that China is one of their biggest existential threats.

Kim Jong un killed off his China-backed uncle and half-brother. President Xi had to wait like everyone else for his meeting with Kim this year. The past 5 years? no meetings. Not to say they are mortal enemies- it's a pretty stable relationship despite all this. But Kim jong un is certainly not a puppet of anyone when he makes decisions.

In the future, I could possibly see North Korea extract concessions from China by reaching out to the US & vice versa - just like they did back in the day with the Soviet Union and China.