Could someone please explain why a lot of the Eritrean clergy are wearing more Coptic looking vestments rather than more Ethiopian looking ones?
Since the Eritrean Orthodox Church achieved autocephaly, I've seen priests and deacons celebrating the Liturgy in both Coptic and Ethiopian style vestments. Ethiopian, of course, because those are the traditional vestments of the region. Coptic, I think, as a show of solidarity and an expression of the extreme closeness and fraternal love of the two churches. I can tell you from personal experience that the Coptic and Eritrean churches are perhaps the closest of all Oriental Orthodox Churches in North America in terms of visiting and fellowshipping with one another. The Coptic Church has stood solidly by the Eritrean Church and given her all kinds of moral and ecclesiastical support, not only when she requested autocephaly from the Church of Ethiopia (which left a lot of bruised feelings on all sides), but also during this current crisis with the unlawful imprisonment of the Patriarch.
I also know an Ethiopian deacon who bought a Coptic tonia and got a blessing from his bishop to wear it at the altar. I don't think it's a big deal. We're all Oriental Orthodox.
Of course, Abune Makarios is attached to the Coptic Orthodox Archdiocese of North America, so His Grace is probably just wearing the vestments he "brought from home".
Is this usual, to see Miaphysites celebrating in Eastern Orthodox temples?
I see it all the time. In fact, if an Oriental Orthodox community is just getting set up in a given city, and there aren't any established churches of our own Communion there to help us out, our next stop is usually the local Byzantine Church. Nine times out of ten, they're more than happy to help us out until we get on our feet.