Victims recant for a variety of reasons. You can't say for sure without knowing the intimate details of how things went down. Often new facts come out after the initial contact with police that indicate that the victim wasn't entirely forthcoming when the police forest show up. For example, victims won't often tell police they started hitting first.
Police in many jurisdictions will overcharge on DV cases just because they want to err on the side of protecting the alleged victim, knowing a protection order will come with arraignment. It's only when they sit down with the prosecutor and interview the alleged victim in greater detail that they determine whether it's a good case of DV. If it's a case where there are injuries, they take pictures so that they can go forward even if the victim recants.