There is the account (story) in one of the Gospels where someone is preaching about Jesus, but is not of the Apostles or disciples directly associating with Jesus, Jesus says to let him carry on, for "whoever is not against us, stands with us" ( I paraphrase), but that is the attitude that must have pertained in the early Church as it grew, and various Sects became evident, called "false Apostles" by Paul, teaching a different Gospel, or set of Doctrines, to Paul.
But nowhere are these Christians called part of the "Kosmos", or World, the world is the people who do not have among them anyone believing in , and teaching the gospel in some form or another, or pagandom we could say.
The J.W org ignores that Gospel story, and lumps together all who are not J.W's, as "the world", which goes against Scripture, and Christian practice.