It isn't really all that strange. There was a great deal of communication between western North America and Japan by the late 1800s. In fact, the US and Japan concluded the infamous Gentleman's Agreement in 1907 because racist policies in California, and the impact of Japanese immigrant labor, had made further Japanese emigration to California, and really all of the West Coast, dangerous and inconvenient. Once Japan opened itself to trade with the West, objects like a katana would have been available and desirable. Also, we now have good evidence that Native American trading networks were very extensive, and metal tools and weapons were highly valued. It is most likely that the guy in question came by it in a trade or purchase with someone who had worked on a ship. It is also very possible that it was an early mass production item from Japan, and that it was made for export, meaning he could have bought it in a store.

Might be a great tale there, but it really wasn't that unusual to find Japanese goods on the West Coast by the 1890s.

You may want to actually link to the picture in your post.