Your argument that the state was acting to "enrich itself" in this instance is not rational. Compare the fine to the costs the state incurred in dealing with this case and it is unlikely the state saw any positive revenue at all. If the goal was to make money, they'd do much better with speed traps, which have lower enforcement and judicial costs and a proportionally higher return.

As to the deterrence, we're talking about a crime involving using a gun to kill. If anything, a few days in jail, a temporary suspension of hunting privileges, and a modest fine are too light a punishment to deter other would-be poachers. Your assertion that these penalties are "heavy" is arbitrary. Please cite other crimes involving firing a rifle at a living creature that were punished more lightly.