Scam? - Anxious - Family facetime call initiated from unknown number

I just had a Group FaceTime with my cousin and me (UK) my aunt (USA) and a number none of us know (UK).

I saw a FaceTime from my cousin and aunt (didn’t notice the other number) so I picked up concerned as my if it was from my aunt then due to her being in USA she wouldn’t call us so early.

My cousin answered first, then I popped on and there was this random person (the person who initiated since me or my cousin didn’t start the call, we don’t have her number and my aunt never answered).

I’m so confused if this is a scam or what and how they got our details, since we live in different countries, the number was also UK based and she sounded from UK too.

I saw an article from a couple of years ago where there was a security risk where people were able to listen to audio and mic from FaceTime calls even if not answered and I’m really concerned and anxious about the whole very weird situation.