Any smoker can cause this. The key thing to know is that a wood fire is a chemical reaction caused by heat+air+wood. It is not an actual thing itself, but is a chemical process of converting these three things into new things.
When wood is heated to a sufficient temperature in the presence of oxygen, it will break down. Notice I did not say "burn" burn is more of a laymans term for what is happening. What is really happening is the wood itself is being broken down into different compounds.
These compounds are ultimately solid or gaseous, and the gaseous compounds float away. What you call "fire" or "flames" is actually some of these gasses being released from the wood, which is not how most people envision them. These gasses just so happen to be combustible, and if there is enough air and heat present these gasses ignite causing the glowing flame you see. If there is not enough heat or air, then you may not see flames at all but instead just see "smoke" which is really just all of the unburnt gases and small particulates being carried away.
So, the first thing to know is, that a fire that is not burning well due to lack or air and/or heat is that it will make a thick smoke, and inside that smoke is a whole lot of chemicals (gases, particulates). A clean burning fire produces very little smoke, and therefore has fewer chemicals.
Wood fires produce hundreds of different chemicals, a great many of them hazardous to your health. Pretty much all of these bad chemicals can be burnt off though in a clean burning fire. So the way to think of this is, a clean burning fire producing a thin smoke is literally burning away the bad chemicals before they get to your food. A dirty fire, one producing thick smoke is going to put all that nasty stuff all over your food.
Interestingly enough, not only can you tell a good clean burning fire by the simple observation of thinner smoke, but the color is different too. A clean fire is a thin blue smoke, and dirty fire is a thick white smoke (or even yellow if really dirty). Here is a picture to demonstrate.