Do please edit or delete this to suit the AUP.
Personally, I think I understand it as meaning..
'That both sides have held an Orthodox enough Christology over the last 1400 years'.
Certainly most ordinary faithful through the last 1440 years have held a similar enough Christology, without too much depth, but enough grasp of the main issues. I would even say that after Constantinople 553 there has been a general consensus in Christology which allows both parties to be Orthodox enough.
I would have to say that in detail I am not sure that all Christologies have always been equivalent. I would, personally, see the OO positions and the EO positions as two overlapping sets, and I would have to say that personally whereas I see the OO positions being essentially Orthodox, I think that some EO positions have been outside the set of Oriental Orthodox positions and also outside the set of possible Orthodox enough positions.
As an example, it seems to me to be conclusively proved that Theodoret was always heterodox in his Christology, both before and after Ephesus I and II and Chalcedon, and yet he is considered a Chalcedonian, and even granted a degree of veneration. Likewise Ibas seems to me to be clearly always a supporter of Theodore and heterodox, yet his heretical letter to Maris was accepted as consonant with Chalcedonianism. This does not make me consider that all Chalcedonian Christologies are heterodox, I don't believe that at all. But some were/are.
On the other hand, it seems to me that canonical Oriental Orthodox Christology does not step outside the bounds of being Orthodox enough at any point. The Christology of Eutyches, for instance, is not the measure of Oriental Orthodoxy, and he was received only on the basis of confessing an Orthodox enough Christology based on the Nicene Creed, on the rejection of any idea that the humanity of Christ was not of the same substance as us, and on a confession that the humanity of Christ was complete. What was of more concern at Ephesus II was the Flavian insistence that to speak of one nature was always heretical, thereby making St Cyril a heretic. Eutyches' opinions were not the main issue.