"Disappointing" refers to the results, not to the person.
The results are disappointing.
The student is disappointed.
The word "got" means "received", and it also refers to the results. This is different from "got" meaning "become", as in "I got confused".
I got [disappointing results]
I was disappointed [ by the results].
NB This is exactly the same as all the other pairs of adjectives formed from verb participles. For example:
I got [some exciting news]
I got excited [ when I heard the news].