Someone told you correctly! When potatoes are stored too long, in a too-cold environment (below 41°F) the starches within convert to sugar. This not only makes for an overly-sweet potato but also alters the cooking chemistry – resulting in uneven cooking performance and discoloration. Store potatoes at home, away from all light sources (to prevent skin greening) and in a cool (not cold) area such as below the counter or inside a pantry. Click here to download a storage fact sheet with further details.