So in Zeugma there is art that is plainly in the Hellenistic tradition. What's more, we can see how style has changed, because there are earlier known mosaics. Remember I wrote some time ago about the mosaic in the tomb at Amphipolis?
This mosaic is at least 100 years before the Zeugma one above. Zeugma is on the Euphrates river, miles from Greece. Amphipolis is in northern Greece (or Macedonia, depending how you think of it).
They're clearly different artists, but they belong to the same stylistic tradition. That's possible because Zeugma was founded by a Macedonian guy called Seleukus, who was one of Alexander's Generals. Seleukus was one of the big winners in the fallout after Alexander's death.
While most of Alexander's successors met untimely and usually pretty gruesome ends, Seleukus survived to found the Seleucid Empire, which was very, very successful. It was largely because of the Seleucid Empire that Greek culture kept its position so far across the Middle East.
It's been known for a long time, by the way, that Zeugma has some astounding art. Up to now the most famous piece has been the Gypsy Girl (not really a gypsy, of course; that's just a name).