During the global pandemic, Taiwan did not lock down, they did not widely test, and yet they have had the lowest death rate per million of any populous country in the world, ranking 189th in the world in the death rate from having only 0.3 deaths per million people. What is the explanation for the continued good health of people in Taiwan?

This indeed is a mystery. This explanation you have seen intuitively is quite simple—they have simply not introduced the virus directly as yet in that nation, so the relatively few cases are due to outside introduction via human carriers. There has not been a concerted program to introduce the virus the way they have done in most other countries. You will see them catch up with the rest of the world because they do not want too many questions asked about such anomalies, not to mention their desire is to harm everyone.