There was also a lot of seaborne trade. Some of it apparently got as far as Japan, through multiple intermediaries, no doubt.
The Romans had connections with ships from Aqaba that went to India for (black) pepper, so it's possible, but it would have gone through many hands as you suggest; it would be easier to simply have one trader take it all the way to Xian, and another from there to Nara.
What interests me is how similar in style and shape this is to Song dynasty wide-and-flat bowls, which eventually become the basis for hirajawan used for drinking tea in Japan in the summer.
There’s a Han court record of a Roman trader arriving in China, and presenting himself as an ambassador (common in ancient times, as a security measure) of Marcus Aurelius. There were of course major seaports in SE Asia that have since completely vanished, but they were a going concern for 1000 years or so, thriving on commerce with China, India, and for a long while, Rome and Byzantium. Islam screwed everyone in the Middle Ages and brought on worldwide economic decline.