I wouldn't call it "coincidence" necessarily. More like "cherry-picking" and "spurious correlations". That is to say, given a very large dataset (like the recorded history of the United States, or the recorded history of Earth, etc.) you can trawl through it and find paths of links like this, where things appear to connect to other things, that connect to other things, etc.
But it's pure post-hoc construction... something akin to creating "just so stories" just with the elements drawn from an assemblage of factual events[1]. There's no particular reason to think that there was any kind of causal connection or other deeper relationship between these events.
[1]: note that in the case of this Lincoln / Kennedy thing, in the forms you usually see this distributed in, it appears to not be the case that all of the individual assertion are true.
But it's pure post-hoc construction... something akin to creating "just so stories" just with the elements drawn from an assemblage of factual events[1]. There's no particular reason to think that there was any kind of causal connection or other deeper relationship between these events.
[1]: note that in the case of this Lincoln / Kennedy thing, in the forms you usually see this distributed in, it appears to not be the case that all of the individual assertion are true.
See also:
https://en.wikipedia.org/wiki/Lincoln%E2%80%93Kennedy_coinci...
https://en.wikipedia.org/wiki/Data_dredging