#Only the bonus disciplines from your order need to be from your order's disciplines
In other words, you are free to choose any psionic discipline from any order, except for the two bonus disciplines you get at level 1 from your order.
Consider the Order of the Soul Knife. It doesn't have any psionic disciplines associated with it, nor does it get these two bonus disciplines (which I think every other order does). However, it still have a number of known disciplines listed in the Mystic table; this is because they can choose anything, so long as it's not their order's bonus disciplines.