Still curious as to why he had two dads, Jon turned on his computer on and went to wikipedia and checked the entry for polygamy and discovered it actually a general term for multiple marriages, "poly-" meaning many and "-gamy" meaning marriage.
Investigating further he discovered that if he specifically wanted multiple "moms" he should have specified the term polygyny in the wish. The alternative for multiple "dads" was polyandry he also learned.
Knowing how unreliable wikipedia could be, he double checked what he had discovered with another reliable reference website.
He quietly cursed himself for not checking his facts before making his wish and letting the stone interpret the wish because he wasn't specific enough. He decided from then on to be more careful about the exact wordings before making wishes.