Popcorn lung is called that because of a specific adulterant which is no longer used in nicotine vapes, and was never prevalent in cannabis vapes.

There is also the risk of getting an illegal cannabis cartridge tainted with Vitamin E, which can be avoided completely if one is lucky enough to live under a medicinal or recreational regime.

It can't be said that vaping is completely harmless, but it's safe to say that responsible blends are orders of magnitude less harmful than inhaling smoke.