lemons on tree are small, like golfball, and turning yellow
What can I do for them to get bigger?
Sometimes lemons drop immature fruit because the tree isn't strong enough to hold all the fruit. There are a few cultural reasons, too. This article should answer questions for you: https://www.gardeningknowhow.com/edible/fruits/lemons/lemon-tree-fruit-drop.htm
I'm guessing that the photo is a mistake, and has nothing to do with lemons.