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.
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).