"the LED [...] will act as a capacitor that charges when light hits it." Wait, what? Photodiodes are supposed to be letting (dark) current through continuously

"the LED [...] will act as a capacitor that charges when light hits it." Wait, what? Photodiodes are supposed to be letting (dark) current through continuously when light hits them in reverse bias. Heck, I even tested it empirically myself, and the light was continuous. On this topic, what kind of light detector is the most linear? Photodiode? Phototransistor? Photoresistor? Something else? I'm thinking about connecting it to a white LED to have an ambient-aware light.