Anarchism

Also, side point, but what is the relation between Stirner and market anarchism ?

My understanding is based on the context the sentence beforehand:

We just need people organizing horizontally one way or another. Ill make it up to Stirner’s ghost later.

I think Stirner could be swapped with any anarchist that had strong opinions. OP says they would be fine with any horizontally organized society, which would get pretty heavy critism from all the anarchists with strong opinions.

And from the top of my head, only relation between markets and Stirner would probably be that Stirners egoism would probably not operate the well in that framework. But I only think so because there is a meme where he just steals a cow instead of using any kind of voluntary exchange mechanism to get the cow: