I think the issue is that the prose isn't clear about what 'an increase in demand' means. It can mean either a movement along the current demand curve due to a

I think the issue is that the prose isn't clear about what 'an increase in demand' means. It can mean either a movement along the current demand curve due to a shift in the supply curve, or it can mean a shift in the demand curve, and those changes correspond to different things in the real economy.