When you learn to cycle, you learn to make microscopic adjustments constantly to keep your bike upright. If your bike starts tipping to the right, you'll turn the bars to the right truly instinctively - you wont be aware of this. This causes your bike to turn ever so slightly to the right and moves your bike back under you i.e upright
doing 40mph down a horrendous slope today , I was making no little adjustments, I just locked my arms (and my butt) and held it rock steady