A recent One Big Happy:
Ruthie has heard her father use the N + N compound student loan but doesn’t know the conventional meaning of the compound (in which the first N functions as Indirect Object: ‘a loan (of money) to a student’), so she (erroneously) gets another possible reading for student loan (in which the first N functions as Direct Object: ‘a loan of a student (to someone)’.
N + N compounds are always interpretable in a variety of ways, but sometimes a particular reading has been conventionalized.
In fact, the conventional reading of student loan goes well beyond understanding the first N as Indirect Object, as you can see from the Wikipedia gloss:
A student loan is a type of loan designed to help students pay for post-secondary education and the associated fees, such as tuition, books and supplies, and living expenses.
That is, a student loan is first of all a loan of money — not, say, a loan of someone’s car to a student for driving to school. And then it is specifically to a certain kind of student (post-secondary, not K-12) and for certain purposes (for covering certain expenses associated with education, but not, say, for buying a house or starting a business).
So there’s a lot Ruthie doesn’t know about student loans.