No. It is unlikely that the context refers to China. Firstly because Isaiah 49 seems to relate to a more local geography and also because the name Sinae is not attached to China at this period. Gesenius favoured China, but other lexicographers have pointed also at Syene, modern Aswan, in Egypt.
The KJV left the Hebrew untranslated as the plural Sinim:
Behold, these shall come from far: and, lo, these from the north and from the west; and these from the land of Sinim. (KJV)
Some modern versions such as ESV have Syene.
11 And I will make all my mountains a road,
and my highways shall be raised up.
12 Behold, these shall come from afar,
and behold, these from the north and from the west,
and these from the land of Syene.”
Although the translators of the the Greek Septuagint were five centuries after Isaiah it is interesting to see them render it as “from the land of the Persians” :
49:12 ἰδοὺ οὗτοι πόρρωθεν ἔρχονται οὗτοι ἀπὸ βορρᾶ καὶ οὗτοι ἀπὸ θαλάσσης ἄλλοι δὲ ἐκ γῆς Περσῶν
Later still the Targum and Vulgate Latin render it “from the land of the south” – though why the South rather than the East is not clear. Perhaps this reflects the geographic focus of the Roman empire rather than the Greek.
In sum fundamentally we don’t know. And in any case it is only a passing reference attempting to give three points of a compass.