"How would you make a magic blanket?" Parson asked, gnawing on a heel of the rye loaf. "If you wanted one?"
Sizemore looked at Maggie, who was nibbling cheese, and spoke up. "That's Stuffamancy. Really versatile magic. Weapons, armor, tools...Stuffamancers just imagine it and conjure it."
"Conjure as in make it?" Parson said with his mouth full. "Create it? Or summon it from somewhere?"
Sizemore leaned forward excitedly, rocking a little as he spoke. "That's a great question, Warlord. There's a big debate about that, getting right down to the level of 'what is magic?' and 'what is stuff?' Some Casters think they're the same thing, and that Stuffamancy proves it. But even the Stuffamancers don't agree about that."
There was a British television serial (remade for America, though inferior) called Life on Mars which featured a modern detective named Sam Tyler who got into a car accident and when he came to found himself in 1973 as a detective recently transferred to the city. Most episodes feature a tension between him debating whether or not he's actually in the past, merely in coma, or something else entirely. This was intentionally left ambiguous by the creators. However, in the last episode (I'll try to avoid spoilers, but reader be ware) Tyler was confronted with evidence that he really was from 1973 and it was in fact the "present" he imagined due to his injury in the accident.
Why do I bring this up? Because Parson entered the world in a way remarkably similar to how Stuffamancy works. The caster imagines the item, and conjurers it. Admittedly, the spell that summoned Parson was a combination of Predictamancy and Findamancy, not Stuffamancy, but to me the implication is there. Parson was not summoned from a different world, but created. His atypicalness is a product of Wanda's lack of proficiency at Findamancy and Stanley's litany of odd requirements for his "perfect warlord."
I'm not saying this as FACT, but rather as an ambiguity Parson may have to encounter. Eventually, he'll realize he has no way to prove Earth existed and that he is merely a product of a spell poorly cast. Hence, Wanda claimed "[Erfworld] wished for [Parson]." To resolve this ambiguity would probably be a weaker narrative, but I'm getting vibes that the authors want to at least explore it.