Why was it fortunate that both Annabeth and Grover stepped out of the car wash during Percy's conversation with Luke?

They meet the God Ares in a diner. He says he wants Percy and his friends to do him a favor. He left his shield at an abandoned water park nearby while on a date, and he wants them to retrieve it. Percy says they already have a quest, but Ares says if they do it, he will tell him something important about his mother. He says he wants Percy and his friends to do him a favor. He left his shield at an abandoned water park nearby while on a date, and he wants them to retrieve it. Percy says they already have a quest, but Ares says if they do it, he will tell him something important about his mother.