As a gay woman - I can only speak for myself. I have ALWAYS been gay, I don't remember ever being attracted to men, and only ever went out with one because it was the done thing - i didn't feel anything for him (Sorry,M!).
I can't speak for others. But I do know that apparently for some women, sexuality is fluid. They don't like labels, they just love who they love, and embrace feelings as they surface. We're a curious lot, women, we like to figure things out, and if that means "giving it a go", then well...women tend to. (and I don't mean that to sound like we are a 'slutty' lot).
People can think what they like - some of the most lesbian women I know (into the parades, activists, etc) were RELIGIOUSLY educated, so I can't agree with Caleb. In fact, whilst I was not religiously educated (eg not at a private school), my early schooling was done in years where homosexuality was still illegal in New Zealand, therefore it was not EVER touched on in my formative years...and hell, look at me.
Perhaps, you could ask them why/how they came to this conclusion - they are the best people to answer this question - NOT US.
As long as people are happy, safe, and not hurting anyone - does it matter?