He needs to consider the long term consequences as well. My father was a life long smoker. When he died we took the furniture he had in the house and cleaned it, The built up tar and nicotine would make you sick. We literally changed the look of the furniture when we were done.This same stuff gets in the animals bedding, on the glass, the bottom of the aquarium, his hands, and the animal itself. So not only is he breathing the smoke he is living in the toxic mess it leaves.
ANY type of smoke from incense, candles, cigarettes, or illegal drugs can be harmful to the reptile.
This is because they are extremely prone to respiratory infections because they lack the ability to cough out waste. The animal could become extremely ill from the smoke particles because it cannot cough them out like many people do when they experience that "smokers cough".
It's harmful in that way, but it will also severely mess with the animals senses. Instinct says that smoke is a sign of a fire, and a sign of danger. When the animal smells that smoke it will become stressed and attempt to flee from the area. It can't really do that in a cage.. so it will further be stressed from the overwhelming smoke smell and possibly expect its demise.
So in other words, your friend is being extremely selfish and uncaring towards this animal.