A couple of times recently I called a couple of people and then left a message on their voicemail, because I'd forgotten that that's just not the done thing anymore.

Both these people called me back later (without having listened to the message I left, obvs), but the thing is, I'm positive at least one of them would not have had my name/number in their contacts. So what this means is, this person saw a missed call from a number they didn't know, and just went ahead and called the number to see who was calling about what.

Do people really do this? i.e. not just call people that they don't know, but call people that they don't know they don't know about something that they don't know whether they're interested in knowing about?

Just what is going through these people's minds?