Let me preface this by saying I once did smoke, but no longer do and have no concerns about being around those that do. Other factors may be involved with those that develop cancer and have in some way been exposed to second hand smoke.
Is Secondhand Smoke as Bad as We Think It Is?
https://sites.psu.edu/siowfa16/2016/10/20/is-secondhand-smoke-as-bad-as-we-think-it-is/
"The American Lung Association states that over 41,000 people die due to secondhand smoke per year—approximately 7,330 from lung cancer and 33,950 from heart disease. I question these facts though because, how can you determine that secondhand smoke was the cause of someone’s death? There are so many factors that go into a person’s death; how can their lung cancer or heart disease definitively be linked to secondhand smoke? It just seems like a stretch to me, especially because they provided no scientific proof."
"This study looked at over 76,000 women and found that there is a strong link between smoking cigarettes and lung cancer, which at this point is a well-known fact, but they did not find a link between lung cancer and secondhand smoke."
"The study, however, only covers the link between secondhand smoke and lung cancer, and doesn’t take into account its effects on asthma, heart disease, and other negative consequences that are generally believed to be associated with secondhand smoke. This study seemingly doesn’t actually have that surprising of a conclusion, as it is already largely believed and known that at low exposure levels to secondhand smoke, the risk will not be that great."
"Out of the 40,000 women who reported never having smoked, approximately 10% of them—about 4,000—reported no exposure to secondhand smoke and only 152 of them developed lung cancer during the follow-up. These numbers are incredibly small, especially compared to the 76,304 participants, and you cannot draw any hard conclusions, especially one that is so strong and contrary to normal thought, from this small of a sample size."
Is Second-Hand Smoke Really that Dangerous?
https://www.psychologytoday.com/us/blog/look-it-way/200907/is-second-hand-smoke-really-dangerous
"The largest and longest study (Enstrom & Kabat) followed more than 35,000 subjects for almost 40 years and found no significant risk associated with second-hand smoke. Similarly, the World Health Organization spent seven years at a dozen research centers in seven countries and came to the same conclusion"
"So, I have to wonder - bottom line - about genetic pre-dispositions to cancer. Are some people hair-trigger loaded to come down with lung cancer if they're exposed to lots of smoke, a little smoke or no smoke at all? It would explain why some people smoke all their lives and suffer not at all while others don't smoke and suffer respiratory disorders. It would also explain why Asians (Chinese and Japanese smoke all the time) don't have the same rate of lung cancer deaths that Americans do."
This ties into the current Draconian anti-vaping movement underway. I don't know of one published autopsy or medical study that definitely shows that vaping, in and of itself, was the cause of death. What the individual inserts into the device, of their own free will or purchases on the street corner is a concern and should be.
Proven unbiased correlation and unsubstantiated opinions are quite different.