Looking for advice on how to handle this, my DM allowed us to create new races as per the race guide, we were allowed to create our own back story for the races as well, so a buddy and I decided to be the same race, and have our back story for the race be one of myth and legend, we live on the outskirts of civilization and in constant hiding when a kingdom comes near we don't start wars and we don't make ourselves known we are nothing but old wives tales at best. our race can pretty much not even pass for any other race so when we join the party we are disguised horribly as humans with "conditions" just for fun, the DM said ok and everyone was fine with having something in the group that they didn't know what it was. all except one person she sat down and had to roll every knowledge, perception, all the time saying our race name that we were only supposed to give the DM because it was agreed our race was unknown but she just said "oh I know they exist" and recanted our back story and then worked in that she had been spying on us forever.
I consider this annoying because we did this for fun and this one person HAS to know EVERYTHING and just spout it out to any npc we meet, thoughts?