Anarchists have governance too which means there is a system. The system is different in how it operates, perhaps more decentralized, but it does exist. Even in Bitcoin there is a system in place. You know those mining fees right? You know those Core Developers? It's a technocratic oligarchy.
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Those two things are not the same of course. If I ignore it, will it leave me alone? If yes, it is not a government.
You can have governance without government. Government means, by definition, that it is not voluntary. I can easily voluntarily join a community and live by their standards. If I don't like them, I leave.
I voluntarily agree to do no harm to others or their property too. Most people do that, and no government is needed. Take any largely populated event. Are laws and the government keeping those people peaceful and their interactions voluntary, or are they doing it simply because that's what is ethical?