You just made a ruling, which is, essentially, every GM's job. Up to Dorat to make his ruling. As players, we should be looking for ways to subvert that ruling in our favour. Sorry, Dorat, it's what we do.
As for Grey taking 20, ambiguity when making decisions as a player gives GMs the wiggle room they need to enforce harsh rulings. It's a peeve of mine as a GM and as a player. Drk should be aware that choosing to take twenty isn't a free success, it represents an investment of in-game time. Most of the time it doesn't matter, but what if the GM suddenly argues that, because Grey decided to take 20, the crew ends up waiting for 2-5 hours, and now Imperial reinforcements have showed up and subsequent encounters and skill checks are now more difficult.
I'm not implying that that should happen every time someone takes 20, but is taking 10 really that bad? :P