A "confession" in this case is whatever a person believes. It may be theistic or atheistic, Christian or Hindu, Catholic or Protestant, LDS or Scientology or Presbyterian or Baptist, and so on.
It's not of the Lord to gossip or condemn other Christians. The Bible sets forth clear instructions on how we are to deal with a Christian who is not preaching/teaching the Word. When people attack other Christians and have not follow those instructions, then they ought not to be condemning others. The Bible tells us to watch the words of our mouth and to guard our tongues, because they can be deadly weapons, and can literally ruin people.