the high GI/low GI debate may not ever end in the bodybuilding community, but from personal experience I don't like going over 30-40g of high GI carbs after a workout as a nap becomes inevitable if I do. Some argue that after a workout, and the state your body is in, an insulin response is unavoideable no matter what carb source is taken in. I personally have never taken in low GI carbs post workout, mainly because adding fat isn't an issue for me, building muscle is.

With the milk, and chocolate milk at that, that he's taking in I'd think he's fine as long as it's something like 2-3 cups. Long as there's adiquate carb intake throughout the 12 hour period before the ride and 12 hour period after the ride, I'm sure glycogen stores will be full.