Akvan:
He does not say that he transmigrated in those 14 as a Sotapanna. He was NOT a Sotapanna back then.
In fact, is is only ‘now’ (i,e. in that life as King Bimbisara when he attained stream-entry under Buddha Gotama) that he became able to become a king of non-humans.’ (before he only ‘resided’ there) and likewise ‘but that I (he) still hope(s) to become a once-returner.’, not before in any of those previous lives . So I see no contradiction here.
That is my understanding.
Metta