There is no records of the romans having contact with China.
There are such records. The Bible discusses silk, and the Romans loved it. The Silk Road was established about 1800-1900 years ago to supply the Roman empire with Chinese silk. Later the Romans attempted to breed their own silkworms.
As for extensive pre-Colombian contact, I would assume based on the exchange of plants, animals, metals, disease, and technology, that such contact would stick out in the historical record. In my opinion it's far more likely that the carbon dating was inaccurate or that the interpretation of the plants as American than that extensive pre-Colombian exchange existed.