Jane (Jon's mother) looked at the video game her body was playing (just before the wish) and shook her head. Then, after turning it off, she made her way downstairs, to get dinner going.
Meanwhile, Jon (who had Jane's mind, with Jon's personality) went to his closet and opened it. A worried look came upon his face, as he saw that (while he had no interest wearing the female-like clothes in the closet) none of the clothes would fit his mom. And, he figured, none of his mom's clothes would fit him.
But there was an easy way to fix that. Jon reached down and grabbed the stone, which he apparently knew about, and wished that his mom's clothes and his clothes would be swapped and re-sized accordingly.
In the blink of an eye, Jon saw normal teenage boy's clothes in his closet, and he assumed that his mom had normal women's clothes in hers.
Smiling that he had fixed the clothing problem so efficiently, he put the stone back down. But then, he wondered if he could use the stone in some other way.
He thought for a bit, then said "I wish ..."