Opening the large version of the photo you can also see that it lacks the red frons, which is a characteristic of the Port Lincoln (along with the yellow underparts).
@WhistlingKite24 "28 parrot" is also used as a general name for the species by some people, so it is possible that the keeper wasn't "wrong" as such but rather using the name in a sense which is uncommon (i.e. not referring to semitorquatus but instead the species as a whole).
