Do you know who his intended audience is? Just because his article got posted here doesn't mean he was writing it for the general HN audience.
Most likely he's writing it for an audience that knows very well the difference between immediate/retained modes. I mean, he's writing it on a blog that's all about graphics programming, game engines, etc. So it would be a bad move for him to define terms common to that field in every article.
I remember an article on the woodworking technique of riving that made it to HN front page, the comments took the author to task for implying riving was invented by Vikings because the article was written for Viking enthusiasts on a Viking enthusiast website.
I don't know, he actually spends half the article explaining the difference between the two. It's just not clear he's going to do that until you get that far. So I think it's strange to suggest that his audience already knows the difference.
Most likely he's writing it for an audience that knows very well the difference between immediate/retained modes. I mean, he's writing it on a blog that's all about graphics programming, game engines, etc. So it would be a bad move for him to define terms common to that field in every article.
Given that, this critique is misplaced.