Let the boxes be B1 and B2.

It it obvious, that under given condition, EITHER box B1 OR box B2 must be empty.

If box B1 is empty, then all 8 indistinguishable balls are in box B2: so, there is only one such distribution.

If box B2 is empty, then all 8 indistinguishable balls are in box B1: so, there is only one such distribution.

In all, there are 1 + 1 = 2 such distinguishable distributions.