Assume he's referring to the thoroughly debunked Japanese formaldehyde study where 1 of the 10 disposable atties tested (that they insanely overheated, well beyond dry-hit land, and anything a human could tolerate) released large amounts of formaldehyde.
Ask your friend if he understands how the lungs work/their response to toxins, if he does, he should understand that human lungs are irritated by formaldehyde in concentrations as little as 5ppm. In others words no human could ever inhale what was generated in the "study". It's akin to burning a steak till its a charcoal briquet and then saying "Steaks are loaded with carcinogens, and therefore deadly".
If anything, you're able to tolerate higher levels of formaldehyde production (and its most certainly being produced) when smoking cigarettes due to the anesthetic effect that the smokes chemical cocktail has on the lungs/airway.