|"Is this all real? Or has this been happening inside my head?"
The topic of this article is of a real-life subject that has been mentioned "in-universe" in a canon source. The Harry Potter Wiki is written from the perspective that all information presented in canon is true (e.g., Hogwarts really existed), and, as such, details contained in this article may differ from real world facts.
Martha Steward, the Squib daughter of Ilvermorny founders Isolt Sayre and James Steward, married the non-magical brother of her friend, a member of the Potomuc tribe who was presumably one of her parents' students.