[NSFW] Was she telling a lie?

Today in the locker room, my friends and I were joking around. We were looking at a picture of a squatting work out plan that featured a woman’s butt. My friend said in response to the picture “The only people looking at this picture is guys masturbating.” As a joke, and knowing that my friends would understand my sense of humor, I remarked something along the lines of “Who says it’s only guys?” The joke passed smoothly just as I thought. It was received with the regular chuckle that most of my jokes get. But then, another friend said “I can honestly say that I have never masturbated in my life.” My immediate response was “Are you kidding?” This was followed by glaring looks from my friend and an awkward shift of topics. Later that same day I brought the occurance up to my boyfriend. He was just as befuddled as I was. He said she must have been lying. Maybe I would understand the need to lie about something like that if she was a very conservative or religious person but she’s not. She started experimenting with guys at a young age and was one of the first of my friends to start drinking. My boyfriend and I are both on the same page in that we acknowledge that we both masturbate regularly. We both understand that it has nothing to do with the quality of our relationship or sex life. I don’t understand how somebody so willing to openly admit to sleeping with some guys or being drunk at a party wouldn’t admit to something as common and natural as masturbation. I also don’t understand why she felt the need to go out of her way to say that. Are my boyfriend and I unusual? Is it just me that is unusual?