Too coincidental to be an accident.
In fact, the spread of birthdays is completely coincidental.
It was purely coincidental that he was on the same flight out of Los Angeles, and that he happened to work down the road from the house she rented.
All of the events leading up to our meeting could not have been coincidental, it must be destiny.
According to the CDC, any correlation between the administration of the MMR vaccine and regressive autism is coincidental, rather than a cause and effect relationship.