For the matching question type, it is possible to display the 'Right answer' in the preview's display options (and this may also be set in the quiz's 'Review options').
When the right answers do display then there is a 'dash' currently used to represent a link between the question and the answer. This is shown here:
There is a quick fix of replacing the dash with an arrow in https://tracker.moodle.org/browse/MDL-48629.
This is a very small change that would help avoid some confusion that some students and teachers feel when they see a dash and mistake it for a negative sign.
If you feel that this might help your students/teachers as well then please vote for the issue on the tracker.