There are a lot of misperceptions pertaining to genetically modified organisms (or G.M.O.s.)
For instance, white button-mushroom, whose DNA has been changed in a laboratory to make a version that doesn’t brown as quickly after being sliced, is regarded—erroneously—as a G.M.O. food. But it’s not.
A G.M.O. is a plant or an animal, whose DNA was altered in a laboratory, by injecting foreign DNA—that is, DNA from another organism.
Similarly, those odd-shaped square watermelons haven’t, at all, had their DNA messed with. They’re simply, grown in a box.