First of all, I would say that they are right, they are following the only ‘real’ teaching. Because there’s only one real teaching – just different ways of expressing it.
Even St. Augustine said, “That which today is called the Christian religion existed among the ancients and has never ceased to exist from the origin of the human race until the time when Christ himself came and men began to call ‘Christian’ the true religion which already existed beforehand.”
All inner spiritual teaching, whatever the Tradition, is aimed at preparing the eye of the soul to open, so that Divine Light can enter and we will be able to ‘see’ Reality – above our sense perceptions, above our foolish prejudices, above our narcissistic ‘reason’. This actual preparation, however, is precisely what is missing from our modern versions of religion. “With a truly tragic delusion,” Carl Jung noted, “these theologians fail to see that it is not a matter of proving the existence of the light, but of blind people who do not know that their eyes could see. It is high time we realized that it is pointless to praise the light and preach it if nobody can see it. It is much more needful to teach people the art of seeing.”