Well, that's those people for whom not teaching or endorsing their particular religion is tantamount to teaching or endorsing atheism. So as a teacher or as an other official of the state you don't have to state that "religion is bunk" or that there is no god and atheism is the more rational position - no, it's enough to not mention God, or Jesus, the Bible, etc. in order to teach/endorse atheism. That means if you don't mention God at least once during math or biology class you have forced atheism on the poor children and now they're faith in God is severely shaken.
But well, to make it short, I don't understand these people either.