
You're joking, right? I hope so, but I'll play along. Water is a liquid (we learned that in elementary school, or through life's observations). There is water in deli meat and deli meat, is unlike crackers which contain a negligible amount of water. Often people also have lettuce, cheese, sauce, or other vegetables on sandwiches. These items also contain a significant amount water. Ever cook down a tomato until it no long steams? I have, it's microscopic relative to it's original size. They are therefore, more liquid-like than say, chips.
It took 0.2 seconds of googling to find, btw.
Obviously, and unfortunately, some TSAs are more lax about screening which is how you've been able to get through. I wouldn't expect it at every airport, especially you, OP.