They’re not really
separate ethnic groups, though. The majority of Eritrea’s Christians are Tigray-Tigrinya people, and there are actually several million more of that ethnolinguistic group in highland/northern Ethiopia’s Tigray region than in all of Eritrea proper. What the Eritrean church doesn’t have is Amhara, another highland Semitic people who make up the bulk of the Ethiopian Orthodox Tewahedo Church and are the traditional cultural elite of Ethiopia (hence when Eritrea was still part of Ethiopia, until 1993, there was at least some level of “Amharization” of the education and political systems in Eritrea province, though nothing as blatant as the Imperial days, when Amharic was enforced over all people; I read a statistic once that something like only 5% of all media in the days of the Selassie monarchy was in non-Amharic languages, despite the fact that the Amharas make up less than half of the population of the country). So the situation is a bit confusing at first in that Tigray-Tigrinya people can be Ethiopians (they’re about 6% of the country, and overwhelmingly Christian), but Amhara people aren’t found in Eritrea. But nevertheless “Eritrean” is not an ethnic group any more than “Ethiopian” is, so it’s a bit overly simplistic to say that they’re different ethnic groups when neither of them are ethnic groups, and there are a large number of the same ethnolinguistic group that dominates the Eritrean Orthodox Tewahedo Church in Ethiopia.
Now that I’ve bored everybody…

I’m so happy to hear that you made it to the Coptic liturgy, Jimkhong! I hope you found it to your liking. About the use of the diptych in the liturgy: It is the same here in the USA, too, so it doesn’t really have to do with the translation or the bishop that you’re under (we don’t really use the term “eparchy”; I don’t know why…maybe because it’s Byzantine? Here is a website of the diocese of Sydney and affiliated regions, where you can see all the other places in Asia that have Coptic churches:
coptic.org.au/home/index.php). The thing is that there is no set list of Patriarchs that must be mentioned beyond those with whom we have agreements with the synods of the other churches to commemorate invariably in all liturgies, and those are Antioch and Eritrea only so far. But I have been to liturgies where the Patriarch of Ethiopia was commemorated (back when it was still HH Abune Paulos). When I asked abuna why he mentioned Ethiopia that time and not any other time, and he said it’s because we had Ethiopians visiting us. So I think the others are mentioned at the priest’s discretion depending on context. I’ve never heard the Catholicos of Armenia mentioned, but we don’t have any Armenians with us here in Albuquerque. We mention St. Gregory the Armenian in the longer commemoration of the saints (the part of the liturgy where the priest says “Verily, O Lord, as it is the command of Your only-begotten Son that we share in the commemoration of Your saints…”, followed by a big list of names…I dunno if you caught this in the liturgy you went to or not).
Coptic liturgy books can be very hard to follow, even for me after 2 years of attending this church. Because there is a lot more going on, for lack of a better way to put it, in terms of prayers and responses and all that in the average Coptic liturgy than there is in the Roman (i.e., the priest is often doing something while the deacons are doing something else, and the people something else), it can seem pretty chaotic if you’re new and don’t know your part as a layperson. The responses are very simple, but do take time to learn. Even we mess up sometimes here in Albuquerque, and we’ve been having liturgy for 18 years now! Usually it’s a deacon who uses the wrong language or the wrong melody for a response (because the melodies change according to the season, or even the date; ex. on the 29th of every Coptic month, which never corresponds to the 29th of any non-Coptic month

, the joyful or “efrahi” melody is used for all responses, but since it is not a specific feast, but rather a triple-celebration of the Annunciation, the birth of our Lord, and His resurrection, sometimes the deacons forget and use the regular melody).
Yes, it turns out that even non-Byzantine Orthodoxy can be quite byzantine.

But you do get used to it after attending for a while. Just like in the Catholic Church, every particular church in the OO communion has its own way of doing things, and since the OO never went through a process of “Byzantinization” like the Eastern Chalcedonians did, we’ve kept the original ways of non-Hellenized Egypt, Syria, etc., which are baffling to some, but just as ancient and venerable as anything in the Roman or Byzantine churches (well, actually quite a bit older than anything “Byzantine”, if you take the founding of Byzantium in 330 AD as the start of the that tradition coalescing around a particular geographic area, as the Coptic and Syriac liturgies had earlier done in Egypt, Syria, Jerusalem, etc., but I digress…often).