“It was just lying there” the finder explained as he recalled the moment and the previous two years of inquiries to understand what it was, along with his frustration of not knowing how it ended up in his garden. Afterwards, and with a look on his face that he expected me to have all the answers, asked, “How do you think it got here?”
As with other such Chinese in appearance artifacts found in North America without supporting contextual information, I could only respond that there are multiple possible explanations
A more informative answer came from the Burke Museum in Washington State, responding to the finder's earlier inquiry and photograph. Paraphrasing... we don't know what it is, but similar objects have been found on the West coast of Mexico and “it should not have been found in your part of the country.”