He's aware the Doctor is Donna's friend, a very dear friend. He's not going to cast aspersion, but he'll continue to put his faith in his own kind. Perhaps that's ego, but that's not uncommon among angels.

He wriggles his hips slightly as she pats him down, then makes a squeak of mock-protest at the pinch. "Ooh! Now who's the cheeky one? Keep that up and I'll have to kiss you again."