Did Ethiopians know much about the state of Christendom outside East Africa before regular contact with Portugal was established?

This is a difficult question to answer directly: we have basically no surviving manuscripts from the early/high medieval period in Ethiopia. This will change in a big way in the 13th-14th century, in conjunction with the flourishing of the Ethiopian state and a renaissance in its Church.

The Ethiopic Church is of course one of the most ancient in Christianity, and was tied into the greater Christian hierarchy from initial evangelization. Most importantly, medieval Ethiopia could not ordain its own priests or consecrate its monks. It depended on the periodic arrival of an abuna or metropolitan, a delegate from the patriarchate down in Alexandria (Egypt). Initially, of course, this was no problem. Coptic abunas brought the power to ordain, but also Christian intellectual culture. Some early texts, like the Book of Enoch, are basically unknown in the rest of medieval Christendom but survive in abundance in Ethiopian translations! It is not a stretch to argue that if the abunas are bringing Christian culture, they are also bringing news of the outside world.

This connection became both more important and more threatened after the seventh century. The cascade of Islamic caliphates across Egypt, Kush, Arabia sharply isolated Ethiopia (Aksum) from the outside world for centuries. We know abunas from Egypt occasionally made it through, but their visits were rare and precious.

Although their mission was theoretically religious, it becomes apparent that there was much more involved. The Ethiopian rulers basically kept a lockdown on the visitors, requiring potential monks and priests seeking orders to come to the royal palace to receive them; prohibiting the abuna from leaving. The reasons for this are lost to history, but you can probably imagine a combination of not wanting the outsider to gain intelligence (for whom?) on Ethiopian society/church, and seeing the visitor as too precious with knowledge to be wasted on traipsing around to monasteries.

So periodically, Ethiopian rulers would have received an injection of news from the outside Christian world, although it would have been necessarily limited to one person's perspective and knowledge. Beyond the royal court, though, the average person would have had basically no way to know.

The Ethiopian revival of the 13th and 14th century brings a lot of changes, especially to the Ethiopian church. A handful of charismatic and talented native emperors and Egyptian abunas headline a state/Church-wide revival of military, monastic, intellectual might. At that point, it seems likely that a few more Ethiopians, though probably still more upper-crust level, are gaining an awareness of the outside world. We have surviving Christian manuscripts again, this time translated from Arabic!

Of course, a 15th century translation from Arabic of a 12th century French text that claims to be written by a 7th century Spanish saint is a book of religious stories, not a status report on Christianity around the Mediterranean. Nevertheless, books don't travel in isolation in the Middle Ages. They are carried from one place to another by people who bring news and ideas and gossip far beyond the text. In that way, the trickle of abunas from Egypt throughout the isolated Middle Ages and then the dynamite abunas Ya'iqob and Salama in the 14th century linked Ethiopia's rulers, at least, to wider Christendom.