Fun fact, most planes are inherently stable, just like paper planes. If there is a disturbance, they will self correct most of the time. For example, glider pilots, if they do something stupid, are instructed to just let go of the controls, and the glider recovers on its own very quickly. Few ways this can go wrong: the wings start to "flap" by vibrating to a resonant frequency, in which case they need to change something, and also spiraling down towards the earth: not because the plane would not recover eventually, but because it might experience high forces that destroy them before recovery can happen.
Few planes are inherently un-stable: meaning they cannot keep flying without constant input, only examples I know of are fly-by-wire modern fighter jets (4th generation onward) and planes with weird shapes like the B2 bomber.
I don't think there is too much control put into these gliders for second to second operations, they are probably just letting it fly forward, with the control being: point it in a very general direction and don't lose contact with it.