"Perhaps a better way of putting it is that smoking has not been proven to cause lung cancer in humans"
Theres plenty of evidence that smoking causes cancer in human cell cultures
One of my former employers makes a range of nitrosonicotines which are used as standards in the testing of carcinogenicity of tobacco and tobacco replacements. Several of the larger tobacco companies purchased them, just so they could test exactly how carcinogenic tobacco actually was compared to a known reference, and whether synthetic tobaccos were an improvement or not.
Tobacco carcinogenicity is known and recognised: if it wasn't, then the companies would not need those chemicals