I agree with David. I'm a native speaker and have no idea what a reduced relative clause is. You just need to know what the sentence means and how it works.

My opinion as both a teacher and a learner: Don’t worry about what a “reduced relative clause is”. This sentence is telling you to listen to these two people who are talking. If you understand that, and can make similar sentences yourself, that is all that matters. Learning or teaching the minutiae of linguistic mechanics is a waste of effort 98% of the time.