A biologist is interested in studying the effects that applying insecticide to a fruit farm has on the local bat population. She collects 23 bats from a grove of fruit trees where the insecticide is used and finds the mean weight of this sample to be 150.4 grams. Assuming the selected bats are a random sample, she concludes that because the sample mean is an unbiased estimator of the population mean, the mean weight of bats in the population is also 150.4 grams. Explain why this is an incorrect interpretation of what it means to have an unbiased estimator.