Are you pretending to know? This is an entire field of study, Paleolithic cave art references and phosphene phenomena, there's hundreds of papers about this. We can verify the scales on cave walls and the distance to optic, literally where someone could stand to reexperience the entoptic.
https://www.researchgate.net/publication/287487106_Does_the_...
It is true that this is a hypothesis that has been made, but it's a reach to say that "we know that's what these are".
It's not simply hypothesis, it's already at the theoretic stage, empirical evidence has been gathered from two fields. Any scientist knows that there are never conclusions, there are only regularities pointing to correlations within limits. These limits have been reached by matching scales.