I don't understand this

I don't want to get into the "apodictically certain" stuff in the post. I'm not sure what the point of even worrying about that is. But I didn't understand this point by Peter Klein:

"Both the Austrian and neoclassical approaches to demand begin with an ordinal preference ranking. But the understandings of marginal and total utility are completely different. For Menger, marginal utility applies only to discrete units of a homogenous stock of a good. The fourth apple is allocated to a lower-valued use than the third apple, and so on. The law of demand follows from the fact that additional units of a homogenous good are used to satisfy lower-ranked ends. Note that for the Austrians, the term “marginal” applies to the units, not the utilities. “Marginal utility” is the total utility of the marginal unit, not the marginal utility of a unit. There is no larger concept of “total utility,” of which marginal utility is a little slice."

The bolded part, specifically.

What is the difference? Why would you make a claim like that? Isn't this just fundamental theorem of calculus stuff? I don't see what the difference is.