What do you think of the "How did you know?" Phrase?What's the most likely scenario when someone says this?

I asked my mother, "Is it true that the mental health clinic gave me a birth date in September 1995?" And she instantly replied "It was a mistake by the mental health clinic" "Why do you feel?" "How did you know? "and I replied" You told me 2 years ago ".

Is it common for clinics to assign the wrong birthdate?Anyways, i checked my photos when i was 1 or 2 and they match with my actual birthdate( 1999 ).