Micro.blog actually is a silo, albeit admittedly not a classical one; it does force you to have a micro.blog account to interact with any publication (i.e. refuses webmentions from sites that are not linked to a micro.blog account). I’d call it an IndieWeb-friendly silo, but a silo nonetheless. And so for replies on micro.blog the same logic can be applied: if the reply is linked to original post on a proper IndieWeb site, then, supposedly, this is a purposeful interaction. If not, well, things are questionable, as with any other POSSE/backlog chain.
Comments are webmentions.