Author is saying a cup of coffee is worth $2 to the customer, but an app is not worth even the $0.50 to that same customer.
In this example, you seem to switch out this comparison where instead you compare the cup of coffee the customer buys, to the amount you could possibly make for a $0.50 app bought by a million people.
Agreed, but the point is that the "total worth" of an app is the total utility that it creates in the world across all its customer base.
Of course you're right that to each individual customer the worth remains less than a cup of coffee; if this affects the app writer psychologically, hopefully the size of his/her bank account will be a consolation.
In this example, you seem to switch out this comparison where instead you compare the cup of coffee the customer buys, to the amount you could possibly make for a $0.50 app bought by a million people.