I’m going to echo korimee, and add that it’s statistics.

When you’re tallying causes of death, like cancer, heart disease, stroke, organ failure, pathogens, whatever; if you factor in whether or not people smoke, smokers die younger from those things, and are a higher percentage of deaths like that as opposed to old age.

Non smokers get those things later, statistically, and have better chances of not only surviving, but recovering. Take stroke as an example. On average, the chances of severe disability from a stroke goes up the more risk factors you have. Smokers are less likely to survive a stroke, and if they do, have worse outcomes when they’re stabilized. Then they have less resilience during the recovery process, leading to worse disability statistically.

The final question you asked only applies obliquely, and others have covered that it would only apply in limited cases. Accidental death, the uptick for smokers is essentially meaningless. For the specific “hit by a bus” kind of accidental death, distraction is how it usually happens anyway, but smokers trying to light up might have a slight extra chance of distraction, but I couldn’t see any data on that with a quick DDG search