As Douglas said - when they arrived they where simply "Stick Pearls" - later the naming shenanigans began
All Biwa pearls are freshwater - - but not all freshwater pearls were Biwa
Are the pearls Biwa - unlikely
Are the pearls Stick pearls - certainly
Were there Biwa Stick pearls - absolutely
Did farmers in other locations misuse\misname other freshwater pearls as Biwa - absolutely
Biwa pearls whilst typically being small irregular baroque shape - were also available as:
Near rounds,
Buttons,
Ovals,
Tooth Shaped,
Sticks,
Fancies - such as Crosses and more exotic shapes,
By varying the shape and size of the mantle tissues implants, it was possible to influence the shape of the resulting pearl.
My gut is telling me these are not a creation of this century - this style was very common towards the mid\end of the 80's and into the 90's. More a sibling than a child of the Internet (for those that consider 1 January 1983 as the internet's birth date)
Here is a picture of a brooch with a genuine Biwa stick pearl from 1980