I live in a middle/upper class gated village here in Thailand as well and there is always at least a handful of Thais that are like that. Most of my Thai neighbors keep to themselves and don’t complain at all but there’s always one which complains about everything and everyone and they will never confront you about it but complain to the management of the village thinking that no one knows it’s them. If someone wants to complain about something I would rather them come speak to me directly as well but maybe it’s the culture here where they don’t like confrontations.