It's simple really. Each character that makes an appearance in a game is provided with a program, which is independent of other programs, for deciding the action of the character, and with a program counter. These mutually independent programs are run in parallel. The speed at which the program advances differs for each character. A character representing the player is endowed with the highest speed of advance, and this character is given the highest priority in parallel processing as well. Interaction among characters is realized by communication among the programs, and an order of priority is assigned to communication among programs. As a result, the game is provided with a greater sense of surprise and the program game is easier to create.

I think what it means is NPCs gain XPs even when you aren't interacting with them directly. I'm not sure why it's surprising.

You can read all about it in this patent. I just thought I'd see what patents have been filed for RPGs and this was the least dull, although this one (in pdf) has cute pictures.