The BMD-300 is based on a Nordic nRF52 chip which does not implement a true hardware reset pin. This pin will default to GPIO unless the application specifies that it should be used for reset. The pin has an internal pull-up enabled if configured as reset.
When the pin is pulled low a software reset is initiated rather than a full Power on Reset procedure. It is also worth noting that the reset is triggered by the falling edge of the reset signal which means the application will begin running after the software reset even if the reset pin is still held low.