You mean the film gets to define it's own reality?
Just like every other film in history.
Unless they're saying something that is in absolute contradiction to what was shown (as opposed to clarifying it,) or we're dealing with an unreliable narrator, or other dramatic device or artistic approach, if the film says something happened, or did not happen, that's the reality.
Well, yeah, pretty much. If we assume Superman isn't lying, to the best of his knowledge, we can be pretty certain he would know. He'd be able to see the exact extent of any, and all injuries he caused someone. Side note, that would have been a nice touch in the post senate bomb scene, if Superman got a chance to speak, and told the EMS what injuries the person he was carrying had.
Back on track, Superman's comment, "I didn't kill those men", seems to be specifically referring to the men KGBeast and his men shot, and burned.
Superman is only seen dealing with on individual.
He doesn't say he did not kill anyone: He's responding to the blame for the massacre itself in this moment.
Obviously just nitpicking/semantics really, but the line remains at least partially ambiguous, as to whether or not Superman killed anyone.
We can reach, and assume it means the war lord survived being slammed through multiple brick walls, but we'd still be assuming, technically. But it's far LESS of a reach than assuming any of the occupants of any the cars Batman destroyed in the chase scene, survived.