The melting point of ice is 0 degrees Celcius, which means it exists as a liquid for any temperatures above 0 degrees. The melting point of salt is approximately 800 degrees Celcius, which is way greater than the melting point of ice. This means that for temperatures below 800 degrees, salt exists as a solid.
The temperature of the area where they were placed we can assume was somewhere between 0 and 800 degrees, greater than the melting point of ice but less than the melting point of salt. This why the ice melted but the salt did not.
I hope this helps!