It means that it is malicious to replace the title with what would have been the subheading because it looks like a clickbait title. Subheadings do not mean that anything can be changed into a title if it is a subheading. The fact is that this thread is now occupied by a discussion of bike yards that has nothing to do with technology.
It's not 'malicious', its relatively standard HN title practice. If you think the submitter got it wrong just email hn@ycombinator.com and they'll take a look at it.
