Strange screenshot experience

Hey people, I own iPhonex and whenever I hold the phone in hand for some other purpose it clicks a screenshot on its own. This is so strange. I have enabled triple tap setting to snap a screenshot. More precisely, when I tap my finger behind the phone thrice it makes a screenshot. I’m wondering how is this possible without tapping the phone is making screenshots on its own!!

earlier, I enabled double tap option for this setting. Situation was far worse because whenever I hold the phone it used to make screenshots. But now I noticed it doesn’t take too many as before after enabling triple tap option. Could someone be able to help me?thanks in advance