On three occasions, Grace utters a statement of the form: I’m a X, not (a) Y.

03.167 I’m a science teacher, not a trauma psychologist.
06.015 I’m a lab coat, not an astronaut.
07.073 I’m a scientist, not Buck Rogers.

This is almost certainly a Star Trek homage. Dr Leonard McCoy frequently says I’m a doctor, not a... and the catchphrase was later used in various forms by other characters in the franchise.

More generally, a templated expression like this is called a snowclone.