That was me, and moderators can comment anywhere, anytime.
When a post is deleted it is not removed from the site.
What does deletion mean for a post?
Deleted posts are usually not physically deleted (that is, removed from the system); they're just hidden (AKA soft-deleted). This means they won't appear in search results or data dumps, and normal users following links to them will see a 404 (not found) page explaining the cause of deletion.
Moderators, and normal users with >=10k reputation, see all deleted posts that they have links to.
Quoted from: How does deleting work? What can cause a post to be deleted, and what does that actually mean? What are the criteria for deletion?
So while you did delete it, now that you posted a link to it any user with 2,000 rep (on a beta site like ours) can still read it.
I just added the comment because I thought it would be helpful (nobody can answer a deleted question).