Voluntary association isn't anarchism by itself. That's just a club or volunteer organization. Anarchism specifically advocates for the replacement of the state with voluntary free association. No, your book club isn't necessarily "Anarchist".

Anarchism is a political philosophy and movement that is skeptical of all justifications for authority and seeks to abolish the institutions it claims maintain unnecessary coercion and hierarchy, typically including nation-states,[1] and capitalism. Anarchism advocates for the replacement of the state with stateless societies and voluntary free associations.

https://en.wikipedia.org/wiki/Anarchism