Some part of my brain is snagging on that orientation line.
I believe the author means it to correlate with the line above. As in, "The Stoics believe that the source of moral authority is Natural Law, and the orientation of moral authority is that it applies universally to everyone." And, "The Epicureans believe that the source of moral authority is human agreement, and the orientation of moral authority is that its application is relative to varying human agreements."
It is not Universalist in the sense that some Christian sects are Universalist (that is, in their eschatology--"all souls end up in heaven").
As for moral relativism, which will no doubt be a charge leveled against Epicurus, the false assumption here is that the victims of a given covenant of justice have necessarily given it their assent. An Epicurean may well argue that slavery was immoral even in ancient Greece, in spite of their social conventions, specifically because the slave was never a party to the 'social contract' in the first place. The first lesson for the Epicurean to draw from this is the necessity of securing protection from other men, by means of self-sufficiency and friendship. The second lesson is this; that when the argument qualifying the idea of justice-by-convention is taken to it's natural conclusion, it is in the end an argument for democracy; for general franchise; for limited government; and for free expression.
The "Natural Law", by contrast will always be a cudgel in the hands of dictators and theocrats, for whom moral certitude forms the thin veneer of respectability concealing their depredations.
Or so I think. ? -josh