|"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.
Fuller's London Pride Outstanding Pale Ale is a Muggle brand of pale ale, brewed, as the name suggests, in London. Despite being a Muggle drink, it was among the selection of alcoholic beverages served at the Hog's Head Inn in Hogsmeade.