If they don't come back you can't ask them why not. That's the point. It's a function of the level of competition. If it's a competitive location and you lose that customer, they're practically gone forever.
I love tech, but if I went to a restaurant and they had that, I honestly wouldn't go back.
They gained 10% from those who stuck around and points to them for working the up-sell on side orders, but how many left never to return? To quantify the value of tabletop ordering systems is not as simple as saying "oh look, a 10% gain in average order value" it's much more complex than that. And without the customer numbers and order value variance it's hard to truly analyze the success of the proposition.