|"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.
There was a bakery at Pudding Lane in the 1660s. Muggles say the Great Fire of London in 1666 started on this bakery, but there is debate among the wizarding community whether it began in this bakery or in the basement of the house next door, where legend has it a young Welsh Green was being kept.