facetime answered by someone else on another device

So it was 11.31 and my partner FaceTimed me which I didn’t pick up as I was sleeping. I woke up after at 11.33 as I heard another call, he FaceTimed me and I didn’t pick it up on time. So I ft’d him back and he said that the first call he made was answered by someone that wasn’t me and then that person cut off straight away. In my call log it says 23.31 incoming call (null) (69 KB). I’m 100% certain I didn’t answer this call and it wasn't me. My FaceTime setting is only on phone number so you can’t call me through my Apple ID email.