Anomaly – A misstatement or deviation that is demonstrably not representative of misstatements or deviations in a population.
So its a mistake detected while examining units in selected sample. Such mistakes are not expected to repeat in population (that means not representing population). Example cash payment without approval at the time of earthquake, such mistake is not going to repeat as earthquake didnt happen again and again through out the year.

So such mistakes are not considered while projecting misstatement in population.