This keeps happening to me! I wrote a fairly obscure remark about SICP on HN and 2 days later I was on reddit with one of the top comments as my exact comment.
The user in question has also copied a comment about chili from HN, so it's not the first time. Maybe some attempt at providing reputation for his account, but as you say, what's the point?
Or maybe just some guy harvesting imaginary internet points.
Some kind of spamming operation? I have no idea.