I don't know how things work in Australia, but in the US most of our laws come from court decisions, not from a governing body. We don't like to dream up new laws and write down the specifics, so we just write something vague and use whatever a judge decides it means when it comes up in court. That's why the attorneys on TV shows are always saying things like "But Your Honor, in People v. Swizzlestick it was ruled that...". Something a judge ruled ages ago may still apply, if the ruling hasn't been overturned in a higher court, or contradicted by another case.
In the case of the Ft. Collins law (and the one in Denver County banning feeding ice cream to a donkey on a Sunday), it means that someone actually did those things, and wound up in court for it. The judge ruled that some vaguely-worded law applied to the case (probably something like "Zoo animals are the property of the zoo"), and the person was convicted under that law. So, forevermore, there's a legal precedent for convicting someone of tying a giraffe to a telephone pole.