Well with that low of mileage I would guess it only gets used on numerous short drives?! If so then it could be possible. The engine heats up just enough then gets shut down. This creates moisture and moisture is going to pool in the low spots. In an exhaust system generally the muffler or cat because the rounded parts of them are lower than the exhaust line. Some mufflers are designed with a small hole to let moisture like that out of them.