It is not the same as what
@Maxperson and
@Bedrockgames are describing, because they both do contemplate the GM engaging in fictional creation during the play session. Maxperson especially. (This is why I keep getting confused by their repeated use of "we" and "our".)
In the style you are describing, when the players move their PCs from square to square of the map, and ask questions about what they see and are told things by the GM, they are very much learning what is in the GM's notes. In X2, for instance, the players learn about the different members of the Amber family, they find the portal to Averoigne, they find the ingredients they need to recover Stephen Amber's tomb, etc. There can't be any "exploration" without the GM telling them about these things.