Actually get that a lot at my shop, but it's not always true. A really good, fresh cup of coffee can taste just as good as it smells, maybe even better. The bitterness @jake_kelly24 mentioned usually comes from over-extraction, like using water that's too hot or letting it brew too long. That barista's silence might have just been them trying not to explain coffee science at 7am, lol. A proper cup balances the roast notes with the natural sweetness, so it's not just bitter water.
Ever notice how that first smell of coffee is like warm cookies but the taste is just bitter water? Our noses pick up all the sweet, roasted notes from the beans. But then our tongues get the full hit of the actual brew, which is just kind of sharp and acidic. The smell sets up this promise of dessert that the drink itself can never really keep. That barista was probably just tired of getting philosophy questions before their morning caffeine.