According to lore, a Cambion is the offspring of a man/woman and an succubus/incubus. A succubi supposedly steals a mans semen and then it either assumes the form of an incubus to impregnate a woman.
This would imply a sexual union, not something akin to possession. It can also be implied that the succubi/incubi have a reproductive strategy, as they can?t reproduce on their own, they have established a symbiotic relationship with humans to ensure the reproduction of their ?selfish? genes, manifesting itself as magical potential, proudness, attractivness, and wickedness.
So going by lore, your mother being hypothetically possessed while pregnant with you, would not make you a Cambion.
Now, personally I don't believe that a spirit can do such as impregnate someone, at least these days. My views on Cambions have more to do with the mythos that traditional withcraft draws from.
In traditional witchcraft, Cambions are those who have the witchfire, or the mark of Cain, at birth. It is the blood of a witch. It is an ethereal and non-corpreal signature that some are born with, an affinity for sorcery, yet others are passed on this knowledge (from spirit to person, from man to woman, or woman to man).
It was said that Merlin of Arthurian myth and Cain of the Abrahamic mythos were Cambions.
For Merlin, the first concrete mention of him being a Cambion is that of Le Mort d'Arthur by Sir Thomas Malory in 1485, although there is some evidence he was considered a demigod in some older versions.
This makes it important to remember that any supernatural being or spirit was considered a demon by the Church.
As for Cain; In certain rabbinic lore, we come across the notion that Cain was not the son of Adam, but of the watcher Samael. It was thought that when Samael appeared to Eve as a serpent, he seduced her, the fruit of that union was Cain. Now Samael was a watcher, essentially the closest thing in Judaic mythos to the Christian Lucifer.
Similarly, this continues into the tale of Tubal-Cain, his decedent. It was said the watchers were the luminous beings that taught men sorcery, makeup, war, metal working, and horse-riding, among other things.
At least a few early Christian sects, those of Gnostic Christianity, held onto this mythos as apart of their canon. Modern Luciferian and Traditional witchcraft paths often use this, Cain being a hero figure or even a god.
The Cultus Sabbati has produced an entire book dedicated to this subject, the Psalter of Cain.