I just noticed there is a "Gun" (County) in Daegu...?

Since Daegu is a metropolitan city, all administrative districts below it should be "Gu" (Districts).
But I just happened to find out that there is a "Gun" called Gunwi-gun?
I looked it up and saw that it was incorporated into Daegu a few years ago,
but I'm curious why it remains a "Gun" even after being incorporated...
Since it is a sub-division of a metropolitan city, I thought it would naturally become a "Gu".