I think it was already clear from the morning news reports that there was no actual intruder and this was being discussed at Johnson's office the next morning. Everyone was still giving him the benefit of the doubt at that point and most news reports were saying that OP mistakenly "thought" there was an intruder inside his house and shot his girlfriend. Even OP admitted to the Standers and everyone else who arrived on the scene that he had mistaken her for an intruder. He never said I think there must have been intruders and they got away before I could shoot them, and I accidentally shot Reeva instead. Wonder where those intruders got off to? Please, we better go look for them, they can't be far.
It's quite clear to me-- Michelle Burger and her husband were confident that what they heard must have been Reeva's blood curdling screams before the four shots were fired, and consequently, upon learning the next morning that there was no actual intruder and they were mistaken in thinking what they heard was a home invasion, then they obviously had to conclude that Oscar would have also heard Reeva screaming before he shot her. So yeah, they knew Oscar was lying and felt obligated to contact the police and give their statements.
Despite the smarmy badgering from Roux, Michelle Burger was an excellent witness and there is no reason to question her testimony about what she did not hear while sleeping. She obviously can only testify to what she did actually hear- she was awakened to sounds of a petrified woman screaming for her life and frantically yelling for help, before the blood-curdling screams climaxed just as four shots were fired "Bang (interval), Bang, Bang, Bang". She testified to then hearing a man yelling "help, help, help" three times, but in a flatter affect than the "angst"-ridden cries of the woman.
This question only matters if you are trying to position all of the cricket bat strikes AFTER the gunshots and Oscar's cries for help. I believe Oscar chased Reeva into the bathroom with the cricket bat, yelling "Get the f-- out of my house!" and she locked herself in the toilet for safety, he proceeds to bash against the door unsuccessfully, which pushes him over the edge, so he goes back to the bedside and retrieves his pistol, returns down the passageway and being the well -trained marksman that he is, he knows to pause at the corner of the bathroom wall and fire from a protected location to avoid ricochets. After firing four black talon type rounds into the tiny cubicle and hearing silence from the person inside the toilet, Oscar then realizes he has a situation on his hands. His mind quickly thinks he better reframe the scenario and he goes to his bedroom balcony and shouts for help. He then returns to the bathroom and picks up the bat again and pries out a panel to access the key and open the toilet door. He sits with the dying Reeva for an unknown period of time before calling a friend to come help him carry her out of the bathroom. You know how it goes from here.