The answer is… it varies. I can usually tell ethnicity fairly well, but I’ve been wrong many, many times.
I can’t always tell an Ecuadorian or Peruvian from, say, a Filippino or a Vietnamese.
I can’t always tell an Iranian or a Pakistani from a Mexican.
I can’t always tell an Arab from a Puerto Rican or a Hungarian.
Even within “North Africa,” there are a LOT of different looks. Did Omar Sharif look anything like his fellow Egyptian Anwar Sadat?