That's right, it's sensing your torque input on the wheel, not your touch or squeezing pressure. If you hold the wheel with one hand and let it support the weight of your arm, that usually provides enough torque to prevent the nags. You can hold the wheel with two hands, but then you have to make sure one hand is pulling down a little more than the other to stop them cancelling each other out.
It's slightly annoying that you have to do this and it would be better if there were additional touch sensors on the wheel, but it works okay when you get used to it.