Have you ever seen a Japanese hoe that is that shape? That looks African. I tried to look for old Japanese hoe's but couldn't find any that weren't straight.
I hope no one checks my browsing searches for Japanese Hoe!!
I could not find any examples from his era at all, but as I mentioned, it could very well have been straight when it was a hoe handle and was bent into the shape we see now. I did find quite a few examples of hoe handles from less developed areas that resembled the one in the pic I posted, with the thicker downward curve at the business end. I think it's impossible to know for sure, but all things considered I see know reason why that bokken couldn't have come from a hoe handle if that's what's being claimed.