I took a quick skim. By toxic atmosphere, they mean as in probable health hazard, not as in directly killing people immediately.
Indoor co2 levels can easily hit 1000+ ppm co2, especially if your dwelling is well sealed, as many energy efficient dwellings are. Submarines keep co2 at the thousands ppm for extended periods and were the impetus for co2 studies on how much humans can take.
I don't think a major concern of rising atmospheric co2 is the direct threat to health caused by elevated co2 levels. I, personally, would be angered if someone told me that high co2 levels were dangerous to human health and then I read this.


