Why would facebook notify me that someone was nearby?

[Minh]

It notified you because your settings are default to tell you that. Facebook allows this so you know your friends are nearby and allows you to catch up with them (afterall they are nearby). Other people don't get notified because either those two people are not nearby the other people or that they changed their Facebook settings that nearby friends notifications are off. You don't necessarily have to be subscribed to them to be notified they are nearby but just be friends with them, that is why.

SOLUTION

If you like this to stop go to your Facebook setting (top right hand corner), go to the setting where it says nearby friends and uncheck this.

Hope this helps, if it does vote best please, thanks.