It just seems strange to me that Amber was traded from the Baltic Sea all the way to Babylon, yet there was no trade from China making its way to the Persian Empire? If the Persians knew about China, I assume Herodotus would have also. Was China really that isolated?
"As far as India, Asia is an inhabited land; but thereafter, all to the east is desolation, nor can anyone say what kind of land is there."
Also title typo, uninhabitable desert.
Considering Herodotus lived around 500 B.C., what ancient trade routes are you thinking about. The ancient silk road trade route that connected China to rest of the world (at least to Persia and west asia) were started after the consolidation of the Chinese under the Han empire (~ 200 BC). Until then the central asian steppes, himalayas and the oceans prevented trade and direct contact.
Hard to imagine, but the Chinese seem to be generally unaware of Indians and vice versa until "The records of the great historian" by Sima Qian around 150 BC. It was around the same time that the Chinese diplomat and explorer Zhang Qian explored and reported about Central Asia and Persia. His explorations formed the basis for the development of the silk road centuries after Herodotus.
The ancient silk road
Didn't trade take the form of a network? I always had the impression that it was individual trade caravans moving along the path of trade, and typically not any direct trade between far off kingdoms, with no one trading along the entire route.