I strongly disagree. You are either gay/bi or you are not. Some who is not gay/bi is not going to experiment.
I strongly disagree with your black & white assessment. That's like saying either you like ice cream, or you don't, but tasting it means that you do.
You can be openminded enough to try something without that defining you for the rest of your life...
I tried a threesome with another guy once. Going in, I had no desire to be with the other guy, but I decided that I wasn't going to avoid anything either. I was going to be willing to see how the session progresses and go with the flow.
Let's say the story ends there. By your reasoning, my attitude makes me bi, because I was willing to experiment.
Nothing happened between me and the other guy. No interest on either side. Neither one of us was attracted to the other so we concentrated on the girl in the middle.
Again, I would call myself straight, but only if I needed to call myself anything at all.