The reading you get with a multimeter depends on the design of the antenna
. Some antenna's will read open while others will read shorted.
If you have a reason to suspect a shorted coax then disconnect the antenna and check for the short. On the other hand, if you think that the coax is broken then short out one end of the coax and check for a short at the other end.
What you want is for the coax and its connectors to pass the above tests and the coax connectors to be free of dirt and corrosion