There are various techniques in order to approach a "Stoichiometric combustion" while burning woods. It's indeed very difficult to reach due to various factor (e.g. partially wet woods or mixed woods). The major risk when you have incomplete combustion is the generation of formaldehyde. That's indeed a critical risk but the combustion for "mass heating" is targeting a fast and quick combustion (the opposite of the common "recreational" fire place") where you can limit the risk. Regarding the "carcinogens" and especially the short particles, this is a shared issue among all combustion and the gasoline/fuel burning is also a major source of particles.

So my point regarding this article, you cannot draw risk conclusion without comparing the various combustion techniques.