I think I know how they did it. And this gives one more idea to add for brainstorm. Or actually it extends one of my ideas. Software has to detect quick movement of the touch, quicker than you can possibly drag it. This means only one – you made second touch without raising the first finger. You can calculate where the second touch is because this single position moved quickly half way there. Now you know two positions and you can always calculate where the second touch moves by assuming you don’t move the first touch. Very clever