[danudey]

The distinction is that they won't be monetizing Unreal Tournament 'the game'; there won't be gems to purchase, or hats to buy, or whatever else.

They will be providing a marketplace where other people can sell their own content that they create, which is optional and not (necessarily?) integrated into the main game.

The implication of 'free to play' is that the game itself is full of opportunities to monetize players, or that progression can be sped with currency which you can earn/buy, etc, and that the developer will be splitting their time between bugfixes/features and producing new content to sell to people (at varying levels of balance between the two).

The difference here is that the developers are producing two separate things: one, a 3D tournament-style FPS; and two, a shop where people can sell game content that they've created, and make money from it (or presumably give it away for free).