I need to export differences between two models in Epsilon, I read that Match-trace enables users to export the matches calculated during the comparison,
Are there any attributes (or ways) to export the differences in ECL?
You'll have to clone the Epsilon Git repository  and go to examples/org.eclipse.epsilon.examples.oomerging. It has an Ant buildfile that shows how to use the exportmatchtrace attribute to pass on the trace model to the next E*L task (which could, for instance, produce a model out of it).
The org.eclipse.epsilon.ecl.trace.Match objects in the trace include a "matching" flag that may be true or false. You could try looking at the elements that have the flag set to false and seeing if this matches your expectations.