"Physics" in the context of the article and the game development in general does not mean the natural science. It just means the part of the game that moves stuff around.

Same for the "AI", it only means the part that tells the "physics" when to move the stuff around.

And content is necessary for games but so is the air and food for everything. We don't usually talk about food when discussing technical issues in some field. Just because it's necessary does not make it relevant to the discussion.