I know it was cruel, but I can just see in my mind a very curious 9-year old doing an experiment without thinking of the consequences to the turtle. He may not have even believed the balloon could cary the turtles weight.
That was my first thought, too. How many kids have done silly things to animals without thinking about how it might hurt them. My sister flushed her live fish down the toilet when she was little, and then bawled and bawled when it didn’t swim back. (She said she was putting him on the waterslide or something). This kid might have thought the turtle was going to have fun. Seriously, somewhere a little kid is watching the news and thinking... “They are coming for me and putting me in jail...”
As someone else mentioned, no one put a fire cracker in its shell or anything; this was non-malicious intent, if you ask me.