exporting final master in 48k 24bit - confusion

It depends on where you are reading the properties. If the file has already opened in your wave editor (which one?) it is likely you are getting the properties of the wave in that editor, which may have padded out some bits to give itself some elbow room in processing. The file itself saved from Sonar to Windows storage as a wave file may have fewer bytes per sample.
 
If you want to know the bit depth of the file when it is saved to your hard drive that is a little more complitcated. Under windows XP it used to be pretty easy to get this information from a right click > properties>details tab in Windows Explorer, but MS in its infinite wisdom has decided that the only properties the user needs is the stuff you would use to tag and categorize your files. You can calculate the bit depth (not available under details) from the length, bitrate and file size, but the precision of these reported values (second, hundredth of a megabyte, and kilobit) are suboptimal for this purpose. You can use a hex editor to look at bytes 35 & 36 of the file to see how many bits per sample. There is a free utility that can do this for you if you find you need it often.
https://mediaarea.net/en/MediaInfo