"They couldn't have known" means that the law is likely to be misapplied. And why not? Anybody who codes or has made a rules based system knows of unintended consequences of any set of laws.
Of course, you have a large number of options with most games. By construction, there are a relatively small number of correct and enjoyable ways to play a game and a much larger number of incorrect ways that lead to failure. I don't understand how this is even debatable. Are you saying that anybody can just pick up a game controller and everything to be seen and experienced in the game would just play itself out? In fact, what I have just described would be very much like a movie or a book. In that case, I agree, gameplay videos in this case would be some kind of infringement.