The user interface is the part a person actually operates. On a public screen it carries an unusual burden: the person has never seen it before, will not read instructions, is standing up, and will leave the moment it is confusing.
That rules out most of what works on a phone. Targets must be large enough for someone who cannot brace their hand. Gestures must not be required, because discoverability is zero. Text must be readable at standing distance, which is roughly twice what a designer assumes while sitting at a desk. And the interface must return to its starting state on its own, because people abandon interactions mid-way and the next person should not inherit a stranger's session.
The caveat is that the interface people judge is not the one you designed; it is the one after fifty thousand touches. A layout with a control near the screen edge will be operated by a fingernail, at an angle, on a surface with grease on it. Keep interactive elements away from bezels, assume imprecision, and give visible feedback on every touch so nobody presses twice.
Distinct from UX, which is the whole experience including the queue, the lighting and whether staff are nearby. The UI is one part of it.