Yeah, that was a typo on my part. I didn't notice it at first, and it's now been so long since I posted it that I would feel disingenuous editing it. I think someone pointed out the typo in the comments.

It's very common to edit your typo but still leave it there either crossed out, and/or leave an EDIT: and explain what/why you changed it.

It's perfectly okay to ensure your text is communicating accurate information - in fact leaving it may undermine your explanation as certain folks will focus on the error (or others won't notice it and learn something incorrect).

I encourage you to fix the typo; lots of HN exposure means lots of new readers without context to any time that has elapsed since your (really good) article was first posted.