This young man would be considered a devout Christian by most people. He did not view porn, masturbate or play games. However, he was being misled by wrong teaching. He then held onto these teachings not realising that they were wrong because they were not in the bible. Then he got accursed for preaching those doctrines. Finally because of pride, he could not repent of it (which is to turn away), which made it harder to get the demons out of him.
If we preach the wrong gospel we get accursed:
Galatians 1:8 King James Version (KJV)
8 But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed.
When we repent, we must turn fully from our sins and stop doing them, otherwise the spirits will return with more spirits:
Matthew 12:43-45 King James Version (KJV)
43 When the unclean spirit is gone out of a man, he walketh through dry places, seeking rest, and findeth none.
44 Then he saith, I will return into my house from whence I came out; and when he is come, he findeth it empty, swept, and garnished.
45 Then goeth he, and taketh with himself seven other spirits more wicked than himself, and they enter in and dwell there: and the last state of that man is worse than the first. Even so shall it be also unto this wicked generation.