I don't think being bisexual had anything to do with me being poly, personally, as I was heavily closeted from even myself for about 9/10 of my life. Call it a product of my upbringing and environmental factors. I love Texas, but a lot of the people here can take a long walk off a short pier.
I will say that being poly kind of opened the door for me to embrace my bisexuality. I'm really not sure why. It's sort of like "Well, I opened this door... I might as well open the next one and see what's back there! Could be a new car!"
So far I haven't found a car.