Wow, I hadn't realized that people thought the term BIPOC literally meant "Bisexual People of Color" -- although I guess I can see how someone might draw that erroneous conclusion.
My understanding, as you've thoroughly described in this article, is that BIPOC means "Black, Indigenous, & People of Color." (emphasis on the *and*)
Although I can see some people thinking it means exclusively "Black & Indigenous People of Color" -- but that specific usage would really be exclusive, because it would diminish the lived experiences of people of Latino(a), Asian, Desi, Persian/Arabic, and Middle Eastern descent.
You've outlined it in a very clear and educational way...how centering the American government's genocide and oppression against Black & Indigenous people simply enhances the shared solidarity amongst People of Color from all backgrounds.