Meh, this is largely a debate over semantics since the mere notion of a "French people" wouldn't have made sense at the time. "Frenchness" isn't an ethnicity, it's a mix of many different peoples that mixed and intertwined over the years (celts, romans, germanic tribes, immigrants from all over Europe...) and that eventually were all brought together as subjects of the french kingdom.

Normans weren't "french" in the modern sense of the word, but then again very few people in what would later become modern France would have at that time : they all would have considered themselves "Provençal", or "Breton", or "Lorrain" who just happened to live in a Duchy that swore fealty to the king of France.

All things considered, William the Conqueror was a lord of the french kingdom, swore fealty to the king of France and spoke French, so he was no less (but no more, granted) French than any other of his peers. Whether you want to call him french is up to you but is largely an anachronism