The droning and the vocative exclamations are interesting, but listen to the actual melody of the Kyrie eleison. This particular setting dates to the 6th century and evolved into Kyrie XII, used in the Mass below (relevant part starts at 6:25). Here, if anywhere, is an example of liturgical continuity between the ancient and the more recent. The above chant I imagine was still used during the papacy of Innocent III, when the un-Gallicanized Mass was still celebrated once a year by the Pope (a tradition effectively axed by the Franciscans).
Thanks to Marko for bringing the error to my attention. The text has been updated to reflect that the Kyrie in question is XII and not XIII.