OK, that explains the size, and I guess, DCH was right all along!
The your coin is copper or brass. (That's what Krause says, "copper or brass".)
Another thing, I see the denomination under the lion which means that your coin is the "second issue" struck at the Addis Ababa mint in 1922, 1931, and 1933 from the newly prepared dies with the correct denomination. The first issue was done (my guess in 1897) with the dies intended for 1/8 birr, so they either deface the denomination or completely obliterated it.