I wouldn't expect an explanation, I wouldn't say the author is obliged to that kind of effort.
I did sort of expect a link to an explanation, though.
At this writing, other comments in this very HN thread claim there are many intro-level explanations of IVs out there to choose from. They don't link to them either.
Hypertext is what makes the web special, you know? The article would be more useful with a link. Think of this: even this discussion, here on HN, would have been more fruitful if the author had included a link to some explanation.
Similarly maybe the author didn't explain what "IV" means because their audience understands that term.
I have actually shipped a couple of products that made use of encryption packages, and I've never heard of an IV. Maybe the encryption advice I followed was terrible; maybe the instructions were terrible; maybe the packages were terrible. Maybe I'm an idiot suited only to the digging of ditches.