I think you can look at it in the way that in everything in nature there is too little, just right, and too much. Heat, UVB, Vitamin D3, and even water. Literally every husbandry parameter can have the three Goldilock levels. In fact, to truly understand any of these parameters we need to know where those cut off points are.
And we can apply this to air movement as well. Too little air movement and the air is stagnant. It is oppressive to breathe and stinks. Bacteria, fungus, and mold start growing and we have a unhealthy environment.
When air movement is just right the air is fresh, comfortable to breathe.
When there is too much air movement it is annoying and uncomfortable. If it is cooler air then it means we have to work harder to keep our head warm. Our immune system starts getting stressed leaving us to be more vulnerable to opportunistic diseases.
I can't lay out exactly what drafts do to chameleons. I don't know how drafts would affect a cold blooded animal. I imagine it would be similar to us because it cools them, but I have no references to back this up. But if the draft is dry then your humidity will also be a challenge to keep in the comfortable range.
So, in the end, your breeder warned you against drafts because it is considered on the side of "too much" of the critical husbandry component of air exchange. I recommend avoiding drafts as well even though my explanation of it (at least at this time) probably won't convince someone who wants solid proof drafts are bad. But, at least, you can reconcile what your breeder told you with the commonly understood need for ventilation.
