Natural acidity refers to the amount of free fatty acids that the olive oil contains in degrees. The degrees have no impact on the intensity of the flavor, it is just used as a guideline to categorize the oil, not the flavor.
The high acidity in an Extra Virgin Olive Oil is a consequence of the fruit's fermentation, due to excessive ripeness, plague, illness, etc. The manufacturing process is also decisive. Ultimately we can say that the less acidity in the oil,the better the quality.
Castillo de Tabernas' quality controls are extremely rigorous in order to produce one of the few olive oils in the world that have 0.1º natural acidity.