At least to me, he doesn't come off as angry at anyone other than himself for forgetting to fix his About page. In fact, he says several positive things about HN readers:

"the value of a natural feedback system is greater than any promotional value I would get out of submitting things myself."

"...an excellent positive result of the HN barometer"

"I think of HN as a barometer of what people think."

"Thank you Hacker News"

On the whole, the post is about how Hacker News enabled him to get a read on community sentiment about Fret Wars. This is absolutely a positive thing. He's not blaming HN for continuing to think the site is about randomly generated music, he's blaming himself, and praising HN for helping him discover his mistake.

Now if I was a guitar player, I might be offended... :)