The author of article stated it wrong. It's not the time-of-flight that is used as a proximity measure, it is the received signal strength (RSS). By limiting response times to 8 ms just demands better relaying equipment. 1 nanosecond means around 30 centimeters in air and you need very precise clocks (or by measuring ToF by roundtrip times with very precise local timestamping of messages) and much wider bandwidth (500 MHz+) if you want to measure ToF with such precision. Bluetooth doesn't have that functionality.