Call answered on another device (Mac) instead of on my iPhone

So I was receiving a FaceTime audio call from a cousin, and I checked the FaceTime app on the iPhone and it said that the call was answered on my Mac and not my iPhone. At that time I was going for a walk, meanwhile my Mac was in my room. I’m an only child, so I’m the only person who uses my Mac. I don’t know how the call got answered on my Mac and not my iPhone.