Reality and Subjectivity

Let me preface with this: I know this is a bit silly, but I've just been wondering about this for a while.

A quote from the Harry Potter books that keeps appearing in my social media feeds is the quote “Of course it is happening inside your head, Harry, but why on earth should that mean it is not real?” Commonly attached to this has been the insinuation that reality is entirely subjective. Of course, there's the obligatory religion discussion in the comments, but I won't go into those. I'm simply wondering if this quote, used in context as an argument that reality is subjective, commits any fallacies.

Again, I realize it's a bit silly, but I'm curious.