Is it normal that my friend's daughter flashed me?

Long story short I've known this man who was my boss and he just got custody of his teen kids cause their mother gave them up. Well I was over their house for Sunday breakfast and we were in the living room waiting when his teenage daughter put her feet up on her chair and I saw everything because she had no underwear under her nightie. I was shocked and she smiled. I don't think I should tell him cause he'd go nuts.