As for the other submission, I didn't find the slightest indication that the submitter did anything wrong. If you posted your URL to another site, perhaps they saw it there and thought HN might find it interesting? Alternatively, perhaps they had 'showdead' turned on in their profile, saw https://news.ycombinator.com/item?id=33383563 and thought it might do better with a different title? There are lots of ways that post could have been made legitimately.
It's also not clear what the alternative hypothesis is - what are they supposed to have done that wasn't legitimate? I looked at a bunch of their submissions and none of the links had been previously submitted to HN, so this isn't happening routinely.