To paraphrase both the question and the answer I flagged for those who don't want to follow the links:
What is the meaning of the unexpected messages I see output by my program?
Turn them off by doing this...
I flagged it because the definition of "Not An Answer" given in the flagging interface is (emphasis mine):
This was posted as an answer, but it does not answer the question. It should possibly be an edit, a comment, another question, or deleted altogether
To my mind, this answer does not answer the question. It is, however, helpful information, and so shouldn't be deleted and instead should probably be a comment on the question or on another answer.
My flag was deemed invalid. Please may I at this point make it very clear that I'm not protesting the flag or asking for a right of challenge in any way, shape or form and that I'm happy to accept that this flag has been marked invalid and take the flag weight hit. That's not what I came to ask (indeed, I've asked that question before and have accepted with the resounding "No!" I got).
Regardless of the outcome of that flag, why was I wrong to flag this as not an answer? i.e. Did I get this one genuinely wrong; or was it a borderline case; or did I get it right and this was a blip of moderation?
I'm trying to understand whether I should continue to flag other "should be a comment" items in this way. I don't want to generate a swathe of invalid flags, both because (a) I'm a responsible and genuine flagger (my flag weight is a respectable 700+) who's trying to do his bit to clean up and don't want to waste moderator time, and (b) because it obviously hits my flag weight and I like badges.