Well, the term "tuition" refers to a part of the overall university expense. For example, for NYU, a quick search reveals a whopping $55,018 in annual tuition. That's not the total cost, which is higher since you might be paying for room and board, administration fees, classes/credit-hours, etc.

In general, universities in Europe tend to be free, so I agree with you, 100USD per class is indeed tuition for me. But, it is not the US-centric "tuition" of the brick-and-mortar schools.