Still after Leif Erikson.
This is probably not true. No Chinese records from the Ming Dynasty, including Zheng He's detailed logs, mention the Americas. His voyages are well-documented, focusing on Asia, Africa, and the Middle East. It seems really unlikely he was so meticulous with his Indian Ocean exploration but did nothing for the Americas.
The claim basically comes from one guy, Gavin Menzies, who used it to try to sell books. He also made the claim that the Chinese sailed to Italy in the 1400s and basically started the Rennaisance. I am skeptical of any of his claims.
Marco Polo road with them to California well before Columbus sailed for sure.