Jack stops moving, but does not let Barry get in front of him again, if he has to side-step to block his path there, he will, because the look he's giving Barry is extremely searching. He wants to know if the kid actually believes what he's saying. Based on what he sees, he sighs, shakes his head. "No. You're not." Help isn't an insistence that a person you just met is a liar, followed by a vague threat. Whatever Barry intended when he turned up, whatever he was expecting to offer whoever stepped out of that door, Barr is currently not helping Jack.