There were several stories about it. Spielberg wasn't talking to the press when he said this. It was some party talk that got out. Both he and Katzenberg backtracked very quickly. They were both swearing that they'd never work with him and that they'd use their pull to keep their studios away from him.
Spielberg had once offered Gibson the part of Oscar Schindler. There are 'Hollywood stories' about lots of things. I wouldn't put too much stock in it.