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).
Not quite as invisibility since it has its own caveats, emphasis mine.
You are also adept at evading creatures that rely on darkvision. Such
creatures gain no benefit when attempting to detect you in dark and dim conditions. Additionally, when the DM determines if you can hide
from a creature, that creature gains no benefit from its darkvision.
UA: The ranger, revised P. 8
The main difference is that, invisibility does not end when you are detected by other means that are not magical or with special senses but, in the ranger case, the condition/ability ends as soon as the ranger is detected.
The invisibility condition in PHB 191.
An invisible creature is impossible to see without the aid of magic
or a special sense. For the purpose of hiding, the creature is heavily
obscured. The creature’s location can be detected by any noise it
makes or any tracks it leaves.
Attack rolls against the creature have disadvantage, and the creature’s attack rolls have advantage.
Now, about detection; attacking or casting a spell make you lose the benefit as stated in PHB. 195. Also, there is a big difference between dark and dim conditions (PHB. 183). The main difference is that with normal sight you can see the ranger in dim conditions but you are blinded in dark conditions. Therefore, the ranger in dim condition is not treated as if it has invisibility/heavily obscured, the ranger is treated as if in dim condition.
(PHB 195) If you are hidden—both unseen and unheard—when you make an attack, you
give away your location when the attack hits or misses.
(PHB 183) A given area might be lightly or heavily obscured. In a lightly
obscured area, such as dim light, patchy fog, or moderate foliage,
creatures have disadvantage on Wisdom (Perception) checks that rely on
sight.
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.
Thus, against the ranger when trying to detect him in dark or dim light condition, a Dark Elf and a Human are not treated differently, as if they have the same visual capacities.
As an example, by courtesy of Keithcurtis; Robbie the Ranger and Frank the Fighter are trying to sneak past Danny the Drow and Harry the Human in a dimly lit cavern. Harry has disadvantage on the opposing perception on both the sneakers, while Danny only has disadvantage against Robbie the Ranger.
Best Answer
Yes, it does. If you cast Shadow of Moil on yourself, you are in a heavily obscured area, so enemies are "effectively blinded" when they try to see or attack you while the spell is active. As such, you are treated as an unseen attacker (or an unseen target), and correspondingly get advantage on attacks against enemies (and enemies get disadvantage on attacks against you).
This should work even on creatures with darkvision, since the spell unequivocally states that you become heavily obscured to others. That said, this is a bit unclear since the next sentence states "The shadows turn dim light within 10 feet of you into darkness, and bright light in the same area to dim light." - which implies that the reason it's obscured is a magical darkness.
The reason for the clarification in the PHB errata is that in a heavily obscured area (e.g. darkness), you are effectively blinded when it comes to seeing other creatures that are also heavily obscured - but the designers wanted to clarify that you could still see other things that are in lit areas even when you yourself are in darkness.