If he finished a full sushi meal a minute ago, and before that bit of sushi his most recent sushi meal was three years earlier, he could say:
I hadn't eaten sushi for three years. But I've just had a sushi meal. It was delicious.
But he could also say "haven't eaten" and the rest of his remark would clarify.
In natural language contexts English speakers do not experience meltdown or system failure when the optimal tense is not chosen by the speaker. There's a good deal of "slop" or "tolerance" built into the system -- like the proverbial distinction between a Japanese luxury car and a German luxury car. German cars are supposedly engineered to more exacting tolerances but require more maintenance to keep them in tune.
If the speaker had said "haven't eaten" moments after he'd finished a meal, he could be describing the three-year-sushi-abstinence-context for the meal just finished when creating his Instagram "documentary" of the meal.