Another way of interpreting it is this. 5 new ships that anyone can purchase with 'real' money in the store, but backers get to choose one of them for free.
As ED has become an MMO FD need to fund ongoing server running and development through micro-transactions such as selling paint jobs and perhaps soon ships too.
Devs have stated that these ships will be purchasable for in-game credits:
It means that you won't have to pay in-game credits for them, like the free Eagle in the mercenary edition.
Michael