Detect Magic telling someone “it’s chowder” is a cop-out, same as a DM saying “you failed the skill check because you looked suspicious.” If a spell exists to reveal a magical aura, use it to reveal an aura, not to sass the player.

My answer in that case is “You detect no aura” from the non-magical chowder (or maybe they do detect one if it was flavored with prestidigitation), unless it’s an edition where the effect is a cone, and they are sitting across the table from their friend blinged out in magical gear, in which case they are definitely detecting an aura. Several of them. And they’re going to have to take time, focus, and make checks to recognize that none are coming from the chowder.