1)
What is "Mivtzar Tzur"?
1.
Radak: It is a fortified city on a tall rock, mentioned in Yehoshua (19:29) among cities of Asher.
2)
Why did he count the cities of Chivi and Kena'ani?
1.
Radak: Chivi and Kena'ani dwelled in them with Yisrael; Yisrael had not dispossessed them. They paid taxes to Yisrael.