We are talking about definitions of words. Bisexual just means you fancy people of both sexes.
The issue is, I’m not sure everyone agrees with this. The meanings of words aren’t immutable. Language evolves. And, most importantly, it isn’t language which creates identities; rather, people whose identities aren’t represented by language force that language to change or create new language to express their meaning.
I think that’s what’s happening here. For whatever reason, there is a group of people who no longer feel that the word ‘bisexual’ applies to them, so new language has been created to reflect that. Then people like me mosey along and feel like actually, Label B is a better reflection of my understanding of myself than Label A, so I choose to adopt it. Others in my position might do the opposite. It’s messy and irregular, but that’s what language is.
That doesn’t mean everyone immediately knows what the differences between these groups are, or that there is no overlap, because language doesn’t work that way. Categorising people isn’t easy and never has been, not least when discussing sexual identity (which is very personal, and not always predictable, and not static).
What is the point of having words if the words can change their meanings depending on who’s speaking them?
This is a much wider philosophical question! So much art and literature is an exploration of this exact dilemma. Its certainly not novel to this particular debate.