The software of HN forbid to downvote the replies to a comment that a user has made, so seanmcdirmid was not able to downvote you. Someone else had to downvoted your comments.

[In case you are wondering, I didn't downvote you neither.]

[Also, complains about downvotes and accusations of downvotes are good methods to get more downvotes. See https://news.ycombinator.com/newsguidelines.html ]