Obviously the fact that their mothers have the same name triggers PTSD but that does not automatically mean Bruce would not be startled by any other name.A different name in the same circumstance could work because in that moment he sees Kal as an alien who has no selflessness to put a human life before his own.His own father died trying to stop the gunman who could have killed Bruce as well,to see that kind of bravery in despair was not new to Bruce plus he had earlier taunted Superman that only men are brave,just like his father was and here we see true bravery Superman trying to save someone else -resigned to his own death as long as that other is saved.That act alone was enough to give him pause ,obviously Martha is the 'Chekhov's gun' here but the act mattered just as much as for who it was displayed