There's a good chance that the person has automated the activity (it certainly doesn't appear to be done with any thought), but they're technically not a bot.
It's a relatively new feature, but PieFed merges up crossposts that it sees into one post - whether the post you see within a topic is yours or not will depend on the sort type - there's a 'layers' icon beneath relevant posts, and clicking that can get you to the other posts if the visible one isn't the one you want.
If you imagine what it would look like without the merging, the one shown would be the one nearest the top of the screen - so if you're sorting by 'New', then it'll be the newest, by 'Top' and it'll be the most upvoted, by 'Active' then the most active. Because of how much LW dominates, it'll pretty much always be that one.