Which ancestries/races/species are "standard" as PCs will vary by setting and campaign, especially in non-D&D games. In my old Etan game, for example, there have been both PC and NPC goblin and lizardman characters, because those two are among the "standard" for Etan. But there won't be any halflings - they are not present in that world.
Now certain ancestries/races/species might not be available as PCs for one reason or another, while still having named individuals that the PCs can talk to and otherwise interact with in a non-combat, non-hostile manner. These "NPCs" might not belong to the culture(s) or civilization(s) that PCs are drawn from, or they might have only specialized places in the culture or civilization that preclude them from being standard adventuring PCs.
A palace might have a palace dryad, with her tree in the palace garden - very much an NPC fixture when the PCs visit the palace, but not at all someone suitable to become a PC herself.
Or "Grandma Cuprate" in my Brotherhood of Rangers campaign. One of the rules of the Brotherhood is "Be polite to her; she’s a friend of Captain Grey, the head of the Brotherhood." She's also an ancient copper dragon.
Now certain monsters may be disqualified from being PCs because they are implacable enemies of the PCs, with the only non-combat interaction possible falling into the category of "hostile negotiations." If they share rumors, it will be with malice aforethought and the intent to cause trouble. If they negotiate for ransom (in either direction) there is a very large possibility of bad faith in the negotiations. But even they will be NPCs in the sense of individuals who the PCs might talk to, with names or at least titles (e.g. "I am the Mouth of Sauron").
To get back to the OP: If someone told me they believed that only the “standard” ancestries should be NPCs, then my response would be, "I do not understand. What do you mean by that?"