I suppose it's possible this is a very early draft, and he really is just trying to get the events and facts down before he embellishes at all. Some people write that way (not me, but some do). You know this man better than any of us, but I don't see anything wrong with pointing out that so far it lacks depth and imagery that readers would find stimulating. Are you already familiar with the story? If so, perhaps you could point out that it is easier for you to imagine these details since you are already are familiar with it, and that for readers coming to the story cold it is going to require some texture and setting.

If he really wants to be a writer, he better get used to criticism. And you won't do him any favors by lying or covering up what you think, so by all means tell him. Just do so with a degree of tact and you should be fine.

Good luck.