Where does Warren say that he doesn’t know that homosexual behavior is a sin?
He’s separating attraction from action, and saying that being attracted to same sex is far different from having sex with the same sex.
Just as a man might be attracted to a woman who is not his wife, but that isn’t a sin. The sin is when he acts on that attraction, and has sex with a woman who is not his wife.
Similarly, one might also be tempted to steal, lie, cheat, or even kill,but not take the step to act on that.