Ur Kasdim, Civshon Ha Esh?

IN chumash we have most recently been learning about the sentence "...Vayamat Haran Al Pnei Terach Aviv Beeretz Moladeto BeUr KAsdim." This is talking about how Haran died on in Ur Kasdim "on his father's face". Rashi cannot find a mishna on the text in this circumstance so he refers to the mishna about the civshon haEsh to explain that Ur Kasdim could mean that Haran died in the civshon haEsh. The only problem is that there is no texutal basis for this so Rashi finds another answer. Ramban, however, believes that this mishna is true because it is rabbinic tradition and is hinted to in the text, so he goes to prove that this pasuk is talking about the civshon haEsh. His first proof is that Avraham was not born in the land of Kasdim because this is where the descendants of Cham lived, and Avraham was descended from Shem. This goes to show that this is referencing an event and not a place. He further proves this point by stating that when G-d says " hotzeiticha meUr casdim" he does not say "lekachticha", showing that this was done miraculously. He also adds that the text is vague here. There is an outside account where a king imprisoned Avraham and then let him leave- this was some form of miracle, a hidden miracle. This is Ramban's reason for why Ur kasdim must be the miraculous event in the text.