False, they were orriginally grown for the porpose but since they must be grown in a box thir friut is not tasty or edible and theu are mainly sold as decoration.
Thank you for writing that, since this comment is the most accurate thus far it saved me the labor of writing out a full blown summary. That being said two small corrections... One, they were originally grown to ship easier, but since have only been sold as a living novelty/gift. Profiting of the fact that people had to buy a new one once the one they were showing off started to rot. Two, the fruit isn't so much inedible as that there isn't any of it... I've seen one of these opened up and it's basically 85% rind (green stuff). Though from what I've heard the fruit is actually kinda tasty, albeit there was only 1-2 mouthfuls of the flesh. Take care out there!
http://www.whataboutwatermelon.com/index.php/2009/07/how-and-why-square-watermelons-are-made/
and
https://en.wikipedia.org/wiki/Square_watermelon