A very informal way of saying that one heard a different story or explanation from the one just told. A: "Bob said he's retiring to spend more time with his family." B: "that's not what I heard—word on the street is that he was caught embezzling company money." A: "She's just a friend, Janet! I just met her for a couple drinks and then went home!" B: "Yeah, that's not what I heard, you no-good cheating bastard!"