It sounds to me like they're playing up his injury like he took a fall in soccer, purely for optics and narrative. His injury is totally irrelevant to his legal justification to use force in an apolitical, unbiased legal and ethical lens. Its also necessary for survival against the modern internet fueled lynch mob. Most likely he had some bruising which is by definition internal bleeding, the rupturing of petechiae. His decision to shoot was based on seeing the erratic and already aggressive driver ignore commands, dangerously back up into people, ignoring people at her doors and windows as she put it in drive and lurched forwards towards him. No subsequent events can retroactively affect his justification at that point. If she had completely missed him, it shouldn't matter
You are completely right that it doesn't/shouldn't matter in the principle of self defence in which he is clearly justified, but we should be careful not to cede the argument that he was actually hit by the car, which he was, and not just driven at and missed/he dodged it, as at the end of the day what people believe is what matters.
Something else that is important which people should understand is that the officer was a federal agent,
not police. Police have a duty to build rapport and trust in the communities they serve, which often means not shooting in a situation like this, but federal agents are under no such obligation as they are not part of the community. Many people here have been holding the officer to police standards when he was not police but a federal agent.