I have never used it but out of the blue today it notified me that some random number added me. What is it? How or why did they add me
What is FaceTime audio on iPhone?
Where did the notification come in from? Text messages/iMessage? It might be a spam message. I never heard of notifications for Facetime when a random person adds you.
Facetime Audio means Facetime without the Face. Pretty much works like Skype/Viber which uses data to send voice.
As to how or why they added you - I am not sure. It is likely to be a spam message. Just delete the notification and if you get random calls from that number and you do not know the person, you can block the number.
Go to Settings - FaceTime - Scroll down to Blocked - Select New…
As to how someone added you… I'd look into that. Its possible it may be someone you know, but not a number you know them to have.
As far as what FaceTime audio is, its basically the same FaceTime, but audio only. So like a phone call, but it requires internet access.