This is accurate enough. The first human had non-human parents.
The first human had ever-so slightly non-human parents, which were essentially human in all but one minor distinction.
The difference between any child and their parents is exceedingly small.
It is these small changes happening constantly every generation for hundreds of thousands of years that is evolution.
Furthermore, the population was never likely to be more than maybe a few thousand, scattered around.
Incest definitely took place. Maybe not always parent-child, or brother-sister, but certainly any sort of cousin.
Even humans have had plenty of incest. If each generation of your ancestors had a unique individual (consider how many great great great great grandparents you should have, 64) it would get to mean you are descended from more people than have ever lived.
You must have lots of ancestors who were incestuous meaning lots of your relatives technically filled multiple roles in your family.