I know it's not nice or politically correct to call this little kid fat, but it's also not nice for him to dance around in his speedo either.
I'm going to imagine that this is his parents way of getting him physically active.
They went the extra mile to find a way that their son would enjoy exercise.
It's easy to imagine this since they don't speak any English in the video. In actuality they are probably telling him to dance or no dinner.