Your post really got me thinking!
According to what I can recollect from chemistry, the basics of combustion is that oxygen and fuel produces carbon dioxide and heat (heat being needed in the first place). If the combustion isn't complete, i.e. it's lacking oxygen, it will produce carbon monoxide. Since there is no such thing as 100% effeciency in real life, some carbon monoxide will always be produced. And with little oxygen the main product will probably be CO.
With this in mind, and reading a bit critical (as you always should) I find the article not really that relevant. First of all, it's doesn't deal with open fires (I admit that the charcoal grill is completly compareable with the embers I suggested). And secondly the cases mentioned all dealt with zipped up camper tents.
The shelter mentioned was a tipi, and the heat source an open fire. The tipi will allow more air to circulate, and it can't be zipped up like a synthetic tent. If there is a sufficient supply of oxygen there will be little CO produced. But I can agree that in a one man tipi (never seen one) the space may be to small.
I haven't slept in a one-man shelter with a fire, but I have used embers in two-man spruce tipis (which is a PITA to build) and canvas tipis, and I have slept in a lot of lavvos with open fires, I have used meth stoves in snow bivaucs (not for heat though), and spent countless nights in the old fashioned swedish army tents (which are one pole lavvos where the pole doubles as a chimney) with wood burning stoves. And I haven't died a single time!
I will hand it to you though that nobody ever got killed by being catious. And if your unsure, don't sleep with a fire. Feeling dizzy? Can't light a fire? Ventilate, and put the fire out. Provided you have good ventilation and a good height, fire shouldn't be a problem. I will gladly be corrected, and if somebody feels unsafe with a fire I won't blame them. But until now, I've been fine, and the comfort a fire brings greatly overweighs the risk IMHO.