IANAL either, but you are not wrong. I know about this because I was involved in a lawsuit that involved contract law. In order for a contract to be valid it is not enough to have a document with a valid signature on it. There has to be an actual "meeting of the minds". Both parties have to actually intend to abide by the terms of the contract at the time it was signed, which logically implies that both parties have to know the contract's actual content.

The real underlying strategy here is to leverage people's general ignorance of contract law in order to intimidate them into thinking that they are contractually bound when in fact they are not, at least not legally. As a practical matter, the need to pay a lawyer often trumps the actual law (another lesson I learned the hard way).