The more I look at them, both the questions and the answer are just very poorly worded. The first question equates opacity with blocking line of sight when I think we can at least agree that non-magical darkness blocks line of sight to things in the darkness, but not to things outside of the darkness, so is it opaque or not? The second question is more to the point and makes clear that the overall question is specifically asking about blocking line of sight to things outside the area of the spell as opposed to how non-magical darkness works.
The "answer" does not answer this question! It basically just says that the area of the spell is heavily obscured, which is not at all different from non-magical darkness. It also glosses heavily obscured as "impenetrable to vision" which, if understood in the context of non-magical darkness must mean impenetrable to vision targeting things in the area. The answer also implies that if you have darkvision (the ability to see through non-magical darkness) that the area of the spell is not impenetrable to vision, which, no matter how you interpret "impenetrable to vision" can't be right unless by "that area" Dan is also referring to an area of non-magical darkness.
So I'd say the answer, just like the rules they're an echo of, is trading on the ambiguity that surrounds game-terms like "blocks vision entirely", "can't see (clearly?)", and "can't see through", allowing the reader to apply and perceive support for their preferred interpretation, thus preserving, not clarifying, the ambiguity of the text, which is intentional.