The stone had, in fact, granted Jon's wish to the best of its ability. Lacking perspective, understanding, or self awareness, it analyzed the situation in much the same way a computer would; plus something of the naivete of a small child. "Interesting" meant humans were willing to pay attention to it. And the most interesting thing would be what humans were most wiling to pay attention to. But there were many humans, and an average of their perceptions alone wouldn't fulfill the requirements of the wish.
In general, humans seemed to spend most of their perceptions, at least when they were allowed to choose, on various forms of media and entertainment. As such, the stone chose to utilize these as the basis for the wish.
And what better way to make the world interesting than to make their perceptions of media their reality? That way things would be interesting all the time. Different humans found different things interesting, but the stone tried to be all inclusive. Over the next day or so, the people within the stone's radius would find themselves transforming into figures and concepts found entertaining on television, books, the internet, news, pornography, and all forms of media imaginable.
Later, people would speculate that the people transformed were done so according to their subconscious desires. Others said that if anything it was the opposite, and it was some sort of punishment, or at least an assault based on a person's aversions, fears, and frustrations. Still others insisted it was random. They were all right, in a sense. The stone chose to use all these criteria, so as to create as much diversity in human response as possible. After all, the same thing happening over and over again wasn't interesting at all. Likewise, it wouldn't be interesting if no one realized these things were happening, so the stone gave its amnesia inducing effects a miss.
And of course, as the person the wish was granted to, Jon's interest in the subject was most important of all.
