You now need to remember his velocity, his position on the map, the direction of his flight, his altitude, his plane's weight and who knows what else, I'm not a pilot.

You're not wrong per se, but I'm having trouble fathoming gigabytes of data being consumed by these types of parameters. You could probably track hundreds of thousands of airplanes with that much space. The only thing that I could imagine taking up that much memory is extremely detailed airflow simulation.

However, as a rule of thumb, the vast majority of memory data for video games is in most cases textures and geometry, and not so much the simulation. Based on the article, it seems this game streams high resolution geometry data based on your current location on earth, which I would say is the most probable reason it asks for so much memory.