In Soviet parlance, the Soviet Union was a socialist society but could be fairly described as having a communist government. Of course if you're an anti-revisionist or Trotskyist or Judean Popular Front or the like things get more complicated, but my guess is that anybody who self-describes as "communist" will have picked that option regardless of the description, which is, to be sure, weird on a couple of levels. Like most fringe-but-widely-known groups they're used to being described in ways that are slightly off.