It's 99% clear to me now, I'm dumb.
Obviously, the threaded propeller shaft with the plunger is free-floating; Any pressure from fluid would apply a small amount of force to the back of the plunger, stopping it from rotating, keeping it closed. So when you want to open it, a small bit of rotation from the magnetic field starts to open it, and more flow = stronger rotation, that forces the shaft to spin open and keeps the shaft in the open position. Without any flow, it's only held in place by the friction of the threads and bearing surfaces, and gravity.
From this, it's probabbbbly pretty likely you can't close it while there is significant outgoing urine, once started.
And it probably works pretty well for staying closed, such a small mass I can't imagine gravity would do much in the way of rotating the shaft open.
First person here to get one needs to void, and try jumping up and down a bunch, and see if you leak at all after.
Yeah probably no fail-open mechanism...