We really want to recommend comments if there is evidence they exist, because often the comments are sometimes more useful than the OP. Many places say the OP has N comments and then don’t include the comments at all. If the OP is “What should I do in Portugal in September?” the real interesting text to rank/evaluate is the comment, not the question.
Previous to the change, we would already do this for commentCount > 0 and no comment. This change was that we also now complain on (pseudo-markup: interactionStatistic.interactionType["CommentAction"] > 0).
The current markup is a little confusing. What does CommentAction mean there? Does it mean threaded replies that occur later? Looking at the example thread visually, I can’t understand why one middle post has a 1 and another one has a 0.