You aren't dumb. It's their rule that's dumb, which is why the onus is most definitely on them to display it clearly enough when you book.

I mean, if there's something obscure we need to know, like false teeth not allowed or 25m swimming badge required, you'd expect to be told automatically before they take your money.

I suggest giving them a load of shit for this - on the phone is best - and foul up their Twitter page and review sites too. At the very least they'll probably give you some travel vouchers you can use towards a flight.

Have a great trip :-)