Incredible watermelon

One day in this summer I found a watermelon in a backyard of my house. When I saw the watermelon for the first time, I couldn't believe my eyes. This is the picture of the melon. First, let me say that I live in a city, Osaka, and there are never fields around my house. The backyard is a vacancy and it seems to be almost possible to grow crops. The size of the watermelon is not so big but as big as a handall. But I never know who grew it up nor when it was planted.

Last month,unfortunately enough, I saw the watermelon withered when I went through the backyard. I felt sad about that because I wanted to pick it up and try eating it if I could. But it is still mysterious why the watermelon grew up at such a place.