Caveat: I don't think this is incredibly clear from the wording of the spell, so my answer will be subject to some semantic parsing.
No, that errata does not impact the effect of the Darkness spell.
The fact that "darkness" as opposed to "the effects of the Darkness spell" is listed as an example of a heavily-obscured area and that the spell description doesn't describe it as creating "a heavily obscured area" means that errata is kind of a red herring in this case.
The spell description says that a creature with darkvision can't see through it (which requires the logical leap that creatures without darkvision also can't see through it :) ), which means someone in the area of effect can't see out, since that would require seeing through some portion of the darkness.
A more grody scientific explanation would say that since "nonmagical light can't illuminate it," you can't see something unless light bounces off that thing and hits your eyes, and light that does do that would potentially be illuminating something in the darkness, so...no on that front as well (though if your game gets to the point of debating the nature of light itself, you might want to call it a day already).
I see nothing there that implies it is a barrier to vision, just an active and utter absence of illumination.
You are quite right - there is nothing in the spell that says it blocks vision, just that the area is in Darkness.
However, a strict reading of normal darkness means you can't see through that (PHB p.183):
Darkness creates a heavily obscured area. Characters face darkness outdoors at night (even most moonlit nights), within the confines of an unlit dungeon or a
subterranean vault, or in an area of magical darkness.
And a Heavily Obscured area is (PHB p.183):
A heavily obscured area—such as darkness, opaque fog, or dense foliage—blocks vision entirely. A creature in a heavily obscured area effectively suffers from the blinded condition (see appendix A).
Which has been erratad as:
A heavily obscured area doesn’t blind you, but you are effectively blinded when you try to see something obscured by it.
So, darkness (magical or otherwise) creates a heavily obscured area. A heavily obscured area "blocks vision entirely".
Now, while it is clear what this means for "opaque fog, or dense foliage" is simple and straightforward - you can't see into this stuff and you can't see through it to stuff on the other side of it.
Applying this to darkness, however, seems to result in nonsense because, in the real world, darkness isn't a thing. In the real world darkness is the absence of light hitting your eyes from a certain direction. This can be because of an actual absence of light (underground) or because, even though the region is full of light none of it is coming your way (space). But this isn't the real world, is it?
So you have 3 options:
- Darkness works just like it says in the book - you cannot see into it or through it. This would be really cool for a gothic horror campaign even though it would make navigating at night ridiculously hard.
- Darkness (magical or not) works as it does in the real world - you can't see into it but you can see through it to illuminated areas beyond. I think this is what the rules intended even though they and the errata were poorly drafted.
- Normal darkness works like 2. Magical darkness works like 1. There is no support for this in the Darkness spell description but this is how it worked in prior editions.
Its your world - make it fun.
Best Answer
Smoke grenades
In Chapter 9 of the DMG, explosives are introduced as option for the DM to allow in their game. One such explosive is the smoke grenade which is completely mundane and creates a heavily obscured area:
This seems to be the only concrete case of a defined, non-magical technique to create a heavily obscured area currently in the rules.
Note that this is an optional thing that cannot be assumed to exist in every game. Ask your DM if they'll allow it (or some modification of the idea).
Unearthed Arcana: Smoke Stick
There is one option outside the currently released rules in the Alchemist subclass of the Artificer Unearthed Arcana class.
This is not a piece of equipment though, but a class feature. However, it does provide another rule option (albeit in playtest form) that indicates how creating non-magical smoke would/could work.