@xssfox @isomer This is also very common behavior in all sorts of BTLE based sensors involved in bicycling (and I think often running). You can typically roll up beside a cyclist and pair with their heart rate monitor or whatever, with the only limit being that some cheap HRMs only talk to one BT device at a time and their HRM is probably already talking to their phone or GPS device.
(I sometimes wonder if this actually happens in pro cycling, where knowing competitor stats could be useful.)