Yes, there's something with getting friends to upvote and (especially) to post comments in threads. We want people to upvote and comment because they ran across something that they personally found intellectually interesting, not because a friend has something to promote. Promotional use of HN undermines the intended use of the site, which is why these behaviors are against the rules:
https://news.ycombinator.com/newsguidelines.html
https://news.ycombinator.com/newsfaq.html