Is "Metzad" the same as "Metzudah"?
Malbim: No. Metzad is a high hill. It is strong by itself. Metzudah is a fortress built on the Metzad.
Why does Sefer Shmuel mention only that David dwelled in the Metzudah, and here it says only that he dwelled in the Metzad?
Malbim: There it discusses initially, when David lived in the Metzudah, and around it was a wide area called the Milo without buildings. Later, he found it cramped, so he widened his dwelling outside the Metzudah, on the Metzad, i.e. Har Tziyon around it.
Why is dwelling in the Metzad a reason to call it Ir David?
Malbim: Initially only the Metzudah was called Ir David. After David widened his dwelling to the Metzad (Har Tziyon), all of if was called Ir David.
