Yeah speed damage :0. In many cases to be susceptible to speed damage you have to hit a side wall first, but you're also in susceptibility mode when on rope. And then when you hit the ceiling the speed damage is applied, based only on your vertical velocity I think.
If you just try flinging yourself up into the ceiling with rope, it's hard to do more than 18 in speed damage alone, but I guess with the aid of the zook, you got enough speed to do around 27. Definitely out of the ordinary though :V.