That is one theory for what we see. The trick is figuring out whether this is an anomaly or typical of the early universe and determining what mechanism could have led to it happening (whether rare or common). (edit: though notably, theoretical Pop III stars are still only on the order of 100s of stellar masses, not million, so these SMBHs are almost certainly not collapsed Pop IIIs)

Population III stars are speculated to have been very big indeed. And very short-lived because of their near-0 metalicity. But current models do not have them nearly big enough to explain early SMBHs like this. That’s why these observations are so interesting.