the NEX would have to be in bulb mode, the shutter is in the rangefinder's lens (it's a leaf shutter.) it's a little confusing because the author uses the word "trigger" instead of shutter, or shutter release, but regardless, as the shutter is pressed on the film camera's mechanical linkage the sensor in the NEX is switched to B(ulb) to turn on the sensor, then when the shutter button is released the NEX's sensor is switched off. Keeping it on all the time would cause it to overheat after some time.

The small camera market has gone the way of the Dodo thanks to wonderful smartphone cameras.