|"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 exists), and, as such, details contained in this article may differ from real world facts.
During this period, Nicholas Malfoy is believed to have killed many Muggle tenants, disguising their deaths as plague victims. If this is true, it has never been proven, as he escaped censure by the Wizard's Council.