From this reference, what does this exactly mean?

PvP in the upstairs of the Pissing Crone, for example, isn't in view of any NPCs. Would that be OK?

Or should this be seen as, "any NPCs on the map and/or stationed at the other side of an AT which you're very close to"?

If they MIGHT respond, you need a DM present.

In ANY space, public or semi-public, where NPCs might overhear sounds of conflict and run to tell someone or interfere, players should have a DM present before engaging in PvP.

Cheers.

Could you make it more explicit in the referred post, so that it's VERY clear on the subject?

Nuclear Catastrophe If you think there's even a remote chance that an NPC would interfere either way in a combat, or if you're just not sure...don't engage in PVP there unless you can contact a DM who can confirm that he's at the scene.

It already seems clear to me!

"Even a remote chance" includes being able to see the conflict, hear the conflict, and so on. If you have doubts about whether your PvP is in a legit area, ask a DM.

The Pissing Crone is not a place where you can engage in PvP without DM supervision.