Why do some posts on HN not have a user/submitter?

"Another kind of job ad is reserved for YC-funded startups. These appear on the front page, but are not stories: they have no vote arrows, points, or comments. They begin part-way down and fall steadily. Only one is on the front page at a time." quoted from https://news.ycombinator.com/newsfaq.html

That's an ad. Also note that you cannot comment on them, which is abnormal except for [dead] submissions and older submissions.