Contagion used GPS logging to predict who was where an applied a random transmission risk based on that.
The actual origin of the Bluetooth proximity and duration tracking was from FluPhone back in 2010 or so[0]
Human contact networks, and epidemiology is a long standing science COVID just made that apparent for the lay public.
Quarantines have existed for centuries, contact tracing is Victorian (smallpox mostly),social distancing, It was all application of research that largely already existed.
[0] https://www.cl.cam.ac.uk/research/srg/netos/projects/archive...