You obviously saw all of it, after all, you've, 'been to Kalgoorlie.He didn't just chase him down. Apparently he took the day off work, went and waited at an area where the cops apparently told him bikes were 'dumped' and then sped after Elijah. The perpetrator said he tried to force him into the scrub. Elijah stayed on the track and was hit by the 4WD.
It's hard to see how he got such a lenient sentence, but his clean record was presumably major. You can understand the anger, though, considering the cops role in directing him down there (allegedly) and not respecting the crime scene - even though they knew before getting there what had happened. They drove over the tracks, so it became solely about his story matching the only evidence: CCTV footage of him going past at 67KM/H, and the crushed bike and body.
Whatever that means.