Bluetooth signals can sense when another device is close to your device and for how long. If you're on the first floor of a tall building, and someone else is on the 15th, a Bluetooth signal would not log your interaction. That’s not true of other ways to sense interactions, like GPS.
Most importantly, your Bluetooth signal belongs to you and your phone. Using Bluetooth, your data is never stored centrally (“stored centrally” here means, for example, storing user data in a central master database managed by a government or private entity). Instead, random numbers that log your interactions via Bluetooth are stored solely on your own device.