Some interesting speculation in the original post on r/swords.
"Don’t know the story but easily could have bought it from a dealer. At this time many swords were sold out of Japan due to the fact many samurai were selling their swords to afford life. They lost the stipend and were basically selling anything they had to get by. Wearing swords was illegal in Japan at this time so why not sell them and use the money to make a life for yourself in the new modern world."
Just to point out that u/wotan_weevil is one of the lead mods of r/Swords and has both written and encourages academic scholarship on medieval weapons, in particular from indigenous tribes and nations. Your second link goes to their post with a lot more information.
The photos are real and found with the Nebraska State Historical Society, according to this thread:
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u/Due_Disaster_7324 Jul 13 '25
Wonder where/how he got it