Actually, in the alternate timeline, the vagrant died of food poisoning. It turns out the milk he's ingested contained a nasty strain of salmonella...
From the internet:
You don't know that. It would certainly be a great coincidence if that happened.
Anyway, that would not be the same thing for all the gazillions of microscopic lifeforms on and in the vagrent. If the vagrent was disintegrated so would be the microbes in him. If he just died, someof the microbes in him would survive and have descendants that would eventually live in other humans.
And what are the lifeforms which have the most effiect in determining how long humans live? Microbes. Bacteria and viruses.
The two methods of death for the vagrent would have different effects of the genetic diversity of the many different microscopic species he carried, and thus would effect the future evolution of deadly diseases from those mostly harmless forms of microbes. A different evolutin of different deadly diseases will mean that different humans will live or die. A few different indivudal humasns living or dying will men that a few thousand yers later, and for the rest of the existance of humans, there will be a totally different world population.
I quote from my post number 257 at :
https://www.trekbbs.com/threads/worst-character-assassination-episodes.307981/page-13#post-13799407
I note that there are only three classes of humans sorted by reproductive results.
1) Those who have no children.
2) Those who have children but their descendants die out within a few generations.
3) Those whose descendants continue until the end of their species. And after enough generations, each such ancestor will have so many descendants that every member of their species will be descended from them.
Suppose that a time traveller visits a group of hunter-gatherers living several times farther in the past than the period for someone's descendants to become the entire human population. Suppose that he somehow wipes out the entire group. Unless they would have all died without descendants anyway, some of them should have become the ancestors of everyone living in his era, including himself. So the time travellor will never have been born.
Suppose that a time traveller visits a group of hunter-gatherers living several times farther in the past than the period for someone's descendants to become the entire human population. Suppose that the entire little tribe is at the shore when the ocean suddenly recedes and they walk out on the seabed to gather stranded fish, but he warns them to run for high ground.and they do, and so survive the tsunamies which would have otherwise killed them all.
So some of them will become the ancestors of all people living in the time traveler's era. And to do that they will have to marry and have children with people who would have otherwise married and had children with different people. So after thousnds of years their descendnts will completely replace the total population of humans. And thus the time traveller will never have been born.
Think about mcrosopic life forms and how short their generations are and how many generations they have in one human generation. And which lifeforms have the greatest impact on how long humans live? Microscopic bacteria and viruses.
So suppose that a time traveller travels thousands of years in the past and breathes once before returning to his own time. He will bring specimens of long extinct bacteria and viruses back to his own time. And he will take specimens of the bacteria and viruses of his own time into the past and relese them when he breathes.
That will change the evolution of bacteria and virus species in the past. And that will change the evolution of new deadly diseases from previously harmless germs. Thus a number of diferent peole will live or die than would have. And so by the time the time travller came from, there will be a completely different set of living humans. And thus the time traveller will never have been born.