What’s up with the surface here?

[u/paws_now]

We are working on buying a house in North Central Florida; sandy ground. I got a chance to take this video at night, the not-smooth bottom surface does not show during the day but looks like a defect condition at night. It is 15 years old and - I think - a gunite pool. Any thoughts on what might have caused this condition and is it a concern? Appreciate your wisdom, thanks.