Since they didn’t actually define what a first post is, I think it’s borderline illegal contest but not.

I’d argue that the first post isn’t the OP, since making the thread forces that original post.

I’d say they’re both OK, but in the future, “first post” contests should mean the first non-thread starter post, or the second on the page. Otherwise it’s not much of a contest if the OP sends himself a BP to get that epeen. Seems like an exploit of the system that shouldn’t be allowed.