First of all, Eritrea (where Meb Keflezighi hailed from) became independent from Ethiopia in 1993, after a long war. But Eritrea is culturally very closely related to Ethiopia.
When Meb was born, Eritrea was part of Ethiopia, under the horrific communist Derg dictatorship. Since he left Eritrea with his family when he was 12 years old (in 1987), he never resided in an independent Eritrea.
Both Ethiopia and Eritrea are majority Christian, but with a large and growing muslim population. The traditional Ethiopian Church is the Ethiopian Orthodox Tewahedo Church, from which the Eritrean Orthodox Tewahedo Church split and received autocephaly with Eritrean independence in 1993.
Both of these “Tewahedo” (”One Nature” of Christ) churches are not in communion with the Eastern Orthodox Churches, bring considered “Non-Chalcedonian” and “monophysite”. They are often called Oriental Orthodox Churches. However, there are some moves to try to reunite the two families of Churches.
In the United States, immigrants from Eritrea, Ethiopia, Egypt, etc. especially those who cannot find or easily attend an Oriental Orthodox Church of their nationality, or who no longer understand their languages, often may be received into an Eastern Orthodox Church (e.g., Orthodox Church in America, Greek, Serbian, Antiochian, etc.)
I therefore do not know whether Meb is a Eastern Orthodox or a Eritrean Orthodox Tewahedo Christian. But he is an Orthodox Christian either way.