That is a dramatic tomato appearance - wow. You didn't do anything wrong but I suspect that an insect has transmitted a virus to your tomato plant. It's probably the tomato spotted wilt virus, and the younger fruit higher up on the plant will show symptoms too. There isn't anything that can be done to save the plant as the virus is present throughout the plant. If you have other tomato plants, I would remove this one in hopes of sparing the other plants from becoming infected. It seems that the relatively dry, mild spring has resulted in more virus pressure this year in vegetables in the Willamette Valley. You can read about the disease at this link https://pnwhandbooks.org/plantdisease/host-disease/tomato-solanum-lycopersicum-tomato-spotted-wilt