Here's a supposed first-person account saying that she (an Ethiopian Jew) only found out about the destruction of the Second temple when she moved to Israel.
Here's another account.
But Ethiopia wasn't that far away from the rest of the world, and has many adherents to post-Biblical religions. Many traveling Jews passed through it in the late Middle Ages and early Modern age.
Was it really true that Ethiopian Jews were ignorant of the destruction of the Second Temple?