Yeah, well, they apparently found a way. Because the traditional "prefetching" just wouldn't make any kind of sense, we already do that in existing games. All Unreal 3.x and 4.x games use texture streaming which is location based around the player, so you don't store textures in memory for entire level, but just for the segment player is in and has a view of. The rest is streamed into VRAM per need basis as you move around and done by the engine itself.