I don't know why this particular person has gotten involved with this group; people get involved in cults for all kinds of reasons. For example, some people are very lonely, and cults often go out of their way to make them feel accepted.
But I suspect this person's real reason for getting involved with this group is because down inside he is spiritually empty, and he hopes this group might have the answer to his spiritual hunger. You see, down inside we all hunger for God (even if we don't realize it, or even deny it). The reason is because God made us this way; as the Bible says, "He has also set eternity in the hearts of men" (Ecclesiastes 3:11).
In other words, God made us to be His friends and have a personal relationship with Him forever. But when we turn our backs on Him, the empty place in our hearts remains unfilled, and nothing will satisfy it. This person has experienced virtually everything life has to offer fame, money, pleasure, status and so forth. But his experience will be no different from the man in the Bible who ended up crying, "When I surveyed all that my hands had done ... everything was meaningless" (Ecclesiastes 2:11).
Pray for this person, that he may face his need of Christ and turn to Him. And if you have never done so, open your own heart to Christ's transforming love and power.