On what spiritual basis were the Camping false prophesies made, thank you'?

He "says" that he calucated the date by taking the year of the flood (4990 or something like that) and multiplying it by 7000 (God told Noah he would destroy the world in seven days. And also that a day is like a thousand years for God). Somehow he got 2011. It was obviously false and no one should listen to a false prophet. No man, angel, or even Jesus knows when God will come back so why people believe these false prophets i do not know.