Strange phone question

My son and daughter were just sitting in the same room, and my son’s phone rang then at almost the same time my daughter’s phone rang and my son’s went blank (like the caller hung up). Daughter answered but nobody on the other end. A minute or so later the same thing happened. They compared the incoming number and it was a friend of my son.

Son called his friend back and he said he definitely had called my son to finalize golfing plans.

We are on a family share plan, but they have distinctly different numbers. They both have iPhones, and were both most likely connected to our WiFi network.

How the heck would this have happened though since it hasn’t ever happened to any of the rest of us? My other son also has an iPhone and would have been connected to our network and in the same room often.