To me it would actually make more sense if B said 'was' instead 'have been'. In this case B might be saying that they are constantly hungry because of some condition like pregnancy, for example.

It's odd-sounding, for sure. 'have been hungry' implies that the person felt hunger for a long period of time before eating both salads, which is why they ate both. However, 'was hungry' sounds more natural and doesn't change the meaning.

Yes, 'was' hungry is more natural. You were hungry before you ate the salads and you're not hungry any more. The sentence from your English book is different: A: Do you realize what you just did? You just ate both our salads! B: I did? I must have been very hungry. If I hadn't been very hungry, I never would have eaten both our salads. 'I never would have eaten' is not a present perfect - it's a third conditional form.

I think " have been hungry" is more emphatic - have been very hungry : he is so hungry and he still feel hungry although he ate all salads - was really hungry : he didnt feel hungry anymore after he ate