lol, they mean glare from the camera, like when you watch tv from the side in a bright room so you can't really see it that well, or glare from the sun on ice/snow.. glare from the camera he said was causing the leaves to look more yellow than they actually are in person.
and if they plants are really yellow on top like that, it's most likely due to over watering, or I noticed mine did that a little when I gave them a little too many ferts, but they also showed fert burn spots, so if you don't have the burns as well, it's generally from watering too much