Bedrockgames
I post in the voice of Christopher Walken
It is dismissive because it is pejorative (it arose as “just discovering the GM’s notes” in a debate between these two styles of play). What you are exploring is the world the GM is imagining. Notes are simply a tool for tracking the world. And you are also exploring a world that is shaped by player actions in the game as well and the synergy between this and living NPCs and groups the GM is runningIt's not a dismissal. No setting is real. Calling a fictional setting a "world" is a metaphor.
You can't "explore the world" in a RPG anymore than you can "conquer the world" in Risk; it's merely a fictional conceit that overlays what the players are actually doing at the table, which is declaring actions and rolling dice to see how they turn out. The GM merely acts as an arbiter to allow for a wider declaration of possible actions. A module or a pre-defined setting is a tool that many DMs use to help them make arbitrate these choices.