The stranger was just one explaination out of many to explain the chain of events that were about to occur.
You see, it was still the same stone. But over the course of thousands of years, the stone had lost its charge and its potency. Year after year and wish after wish, its power diminished. Soon the stone's essence had to make decisions as to best please the wish granter. The bare minimum to complete the wish was always a priority, and the process would be slow. The more complex the wish or the greater the demands, the stone would take longer to decide on how to do this. Unfortunatly, this led to some awful mishaps to anyone who touched the stone last, as that person would be as if he/she made the wish.
Luckily, if the stone was given enough time to recharge, the wish could be completed much quicker and more fullfilling. For instance, because the stone wasn't used since Jon's Grandpa had possesion of it, Karyn's wish was completed nearly instantaneously. Bending reality to accept the new changes was an impossiblity as the stone lost this ability centuries ago. Karyn would certaintly have some explaining to do when she got home.
