I agree with you in the fact that you can have anarchocommunism under a anarchocapitalist system but not the other way around. But I wouldn't condense the interaction people have purely on contractual agreements. A contract translates to a system that will need to condense and codify. Life is not a bureaucracy. Life is chaotic and filled with relationships.
The angle I see it, especially under this platform is that property is not a thing, less so is intellectual property. In this two cases they are what build the social relationship amongst people. In this case what I am trying to argue is that the mode we are living under is not really capitalist at all--rather it is a gift exchange economy. The stuff I write and reply to are freely given, even if I do not make physical or crypto cash. What I see is the potentiality of making something and been rewarded in a different way: more views, more followers, etc.
(Anarcho-communism doesn't really need an apparatus, and I don't think it ever intended so. If it did what's the point of calling it anarchic? There can be some structure and order, it just has to come from the bottom up. If you cant find an order for people to mutually cooperate then it's not really anarchist society it's just chaos.)
RE: So I encountered an Anarcho-Communist and this is my discussion/debate invitation...