You might want to reread chapter 1, Taddat, "What Constitutes A Hijacked Thread". Commenting on a poster's motivations regarding a comment of his within the thread does not typically fall under the literal definition of a hijacking. Depending, of course, on how relevant the commented upon comment was to that thread.
For a good example of what does actually constitute a hijacking, or attempted hijacking, i refer you to
this post here.