My 20M gf 19F came out as BI. why does it matter?

Just yesterday she came out as bi, putting it in her social media bios and posting about it. I asked her why it matters, why suddenly identifying with it matters, etc. I asked if she wanted to break up with me or try getting with a girl and she said she wants to grow old with me and shes not interested in exploring outside the relationship. I told her that her sexuality shouldn’t matter if thats the case and asked her to remove it from her bio and her posts because it just seems like shes saying “hey ladies im interested in yall.” I had some mutual friends ask about it because they also thought it was weird. My gf is upset with me for being uncomfortable about the whole situation. Am I crazy or what? Whats your thoughts on this?